* [PATCH] MIPS: Work around LLVM bug when gp is used as global register variable
@ 2026-01-18 9:02 Yao Zi
2026-02-02 15:07 ` Yao Zi
2026-02-02 23:23 ` Nathan Chancellor
0 siblings, 2 replies; 4+ messages in thread
From: Yao Zi @ 2026-01-18 9:02 UTC (permalink / raw)
To: Thomas Bogendoerfer, Nathan Chancellor, Nick Desaulniers,
Bill Wendling, Justin Stitt, Thomas Weißschuh
Cc: Yao Zi, linux-mips, linux-kernel, llvm, stable
On MIPS, __current_thread_info is defined as global register variable
locating in $gp, and is simply assigned with new address during kernel
relocation.
This however is broken with LLVM, which always restores $gp if it finds
$gp is clobbered in any form, including when intentionally through a
global register variable. This is against GCC's documentation[1], which
requires a callee-saved register used as global register variable not to
be restored if it's clobbered.
As a result, $gp will continue to point to the unrelocated kernel after
the epilog of relocate_kernel(), leading to an early crash in init_idle,
[ 0.000000] CPU 0 Unable to handle kernel paging request at virtual address 0000000000000000, epc == ffffffff81afada8, ra == ffffffff81afad90
[ 0.000000] Oops[#1]:
[ 0.000000] CPU: 0 UID: 0 PID: 0 Comm: swapper Tainted: G W 6.19.0-rc5-00262-gd3eeb99bbc99-dirty #188 VOLUNTARY
[ 0.000000] Tainted: [W]=WARN
[ 0.000000] Hardware name: loongson,loongson64v-4core-virtio
[ 0.000000] $ 0 : 0000000000000000 0000000000000000 0000000000000001 0000000000000000
[ 0.000000] $ 4 : ffffffff80b80ec0 ffffffff80b53d48 0000000000000000 00000000000f4240
[ 0.000000] $ 8 : 0000000000000100 ffffffff81d82f80 ffffffff81d82f80 0000000000000001
[ 0.000000] $12 : 0000000000000000 ffffffff81776f58 00000000000005da 0000000000000002
[ 0.000000] $16 : ffffffff80b80e40 0000000000000000 ffffffff80b81614 9800000005dfbe80
[ 0.000000] $20 : 00000000540000e0 ffffffff81980000 0000000000000000 ffffffff80f81c80
[ 0.000000] $24 : 0000000000000a26 ffffffff8114fb90
[ 0.000000] $28 : ffffffff80b50000 ffffffff80b53d40 0000000000000000 ffffffff81afad90
[ 0.000000] Hi : 0000000000000000
[ 0.000000] Lo : 0000000000000000
[ 0.000000] epc : ffffffff81afada8 init_idle+0x130/0x270
[ 0.000000] ra : ffffffff81afad90 init_idle+0x118/0x270
[ 0.000000] Status: 540000e2 KX SX UX KERNEL EXL
[ 0.000000] Cause : 00000008 (ExcCode 02)
[ 0.000000] BadVA : 0000000000000000
[ 0.000000] PrId : 00006305 (ICT Loongson-3)
[ 0.000000] Process swapper (pid: 0, threadinfo=(____ptrval____), task=(____ptrval____), tls=0000000000000000)
[ 0.000000] Stack : 9800000005dfbf00 ffffffff8178e950 0000000000000000 0000000000000000
[ 0.000000] 0000000000000000 ffffffff81970000 000000000000003f ffffffff810a6528
[ 0.000000] 0000000000000001 9800000005dfbe80 9800000005dfbf00 ffffffff81980000
[ 0.000000] ffffffff810a6450 ffffffff81afb6c0 0000000000000000 ffffffff810a2258
[ 0.000000] ffffffff81d82ec8 ffffffff8198d010 ffffffff81b67e80 ffffffff8197dd98
[ 0.000000] ffffffff81d81c80 ffffffff81930000 0000000000000040 0000000000000000
[ 0.000000] 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 0.000000] 0000000000000000 000000000000009e ffffffff9fc01000 0000000000000000
[ 0.000000] 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 0.000000] 0000000000000000 ffffffff81ae86dc ffffffff81b3c741 0000000000000002
[ 0.000000] ...
[ 0.000000] Call Trace:
[ 0.000000] [<ffffffff81afada8>] init_idle+0x130/0x270
[ 0.000000] [<ffffffff81afb6c0>] sched_init+0x5c8/0x6c0
[ 0.000000] [<ffffffff81ae86dc>] start_kernel+0x27c/0x7a8
This bug has been reported to LLVM[2] and affects version from (at
least) 18 to 21. Let's work around this by using inline assembly to
assign $gp before a fix is widely available.
Cc: stable@vger.kernel.org
Link: https://gcc.gnu.org/onlinedocs/gcc-15.2.0/gcc/Global-Register-Variables.html # [1]
Link: https://github.com/llvm/llvm-project/issues/176546 # [2]
Signed-off-by: Yao Zi <me@ziyao.cc>
---
arch/mips/kernel/relocate.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/arch/mips/kernel/relocate.c b/arch/mips/kernel/relocate.c
index 7f1c136ad850..12aa0bbdd65e 100644
--- a/arch/mips/kernel/relocate.c
+++ b/arch/mips/kernel/relocate.c
@@ -420,7 +420,18 @@ void *__init relocate_kernel(void)
goto out;
/* The current thread is now within the relocated image */
+#ifndef CONFIG_CC_IS_CLANG
__current_thread_info = RELOCATED(&init_thread_union);
+#else
+ /*
+ * LLVM may wrongly restore $gp ($28) in epilog even if it's
+ * intentionally modified. Work around this by using inline
+ * assembly to assign $gp. $gp couldn't be listed as output or
+ * clobber, or LLVM will still restore its original value.
+ */
+ asm volatile("move $28, %0" : :
+ "r" (RELOCATED(&init_thread_union)));
+#endif
/* Return the new kernel's entry point */
kernel_entry = RELOCATED(start_kernel);
--
2.52.0
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH] MIPS: Work around LLVM bug when gp is used as global register variable
2026-01-18 9:02 [PATCH] MIPS: Work around LLVM bug when gp is used as global register variable Yao Zi
@ 2026-02-02 15:07 ` Yao Zi
2026-02-02 23:23 ` Nathan Chancellor
1 sibling, 0 replies; 4+ messages in thread
From: Yao Zi @ 2026-02-02 15:07 UTC (permalink / raw)
To: Thomas Bogendoerfer, Nathan Chancellor, Nick Desaulniers,
Bill Wendling, Justin Stitt, Thomas Weißschuh
Cc: linux-mips, linux-kernel, llvm, stable
On Sun, Jan 18, 2026 at 09:02:35AM +0000, Yao Zi wrote:
> On MIPS, __current_thread_info is defined as global register variable
> locating in $gp, and is simply assigned with new address during kernel
> relocation.
>
> This however is broken with LLVM, which always restores $gp if it finds
> $gp is clobbered in any form, including when intentionally through a
> global register variable. This is against GCC's documentation[1], which
> requires a callee-saved register used as global register variable not to
> be restored if it's clobbered.
>
> As a result, $gp will continue to point to the unrelocated kernel after
> the epilog of relocate_kernel(), leading to an early crash in init_idle,
>
> [ 0.000000] CPU 0 Unable to handle kernel paging request at virtual address 0000000000000000, epc == ffffffff81afada8, ra == ffffffff81afad90
> [ 0.000000] Oops[#1]:
> [ 0.000000] CPU: 0 UID: 0 PID: 0 Comm: swapper Tainted: G W 6.19.0-rc5-00262-gd3eeb99bbc99-dirty #188 VOLUNTARY
> [ 0.000000] Tainted: [W]=WARN
> [ 0.000000] Hardware name: loongson,loongson64v-4core-virtio
> [ 0.000000] $ 0 : 0000000000000000 0000000000000000 0000000000000001 0000000000000000
> [ 0.000000] $ 4 : ffffffff80b80ec0 ffffffff80b53d48 0000000000000000 00000000000f4240
> [ 0.000000] $ 8 : 0000000000000100 ffffffff81d82f80 ffffffff81d82f80 0000000000000001
> [ 0.000000] $12 : 0000000000000000 ffffffff81776f58 00000000000005da 0000000000000002
> [ 0.000000] $16 : ffffffff80b80e40 0000000000000000 ffffffff80b81614 9800000005dfbe80
> [ 0.000000] $20 : 00000000540000e0 ffffffff81980000 0000000000000000 ffffffff80f81c80
> [ 0.000000] $24 : 0000000000000a26 ffffffff8114fb90
> [ 0.000000] $28 : ffffffff80b50000 ffffffff80b53d40 0000000000000000 ffffffff81afad90
> [ 0.000000] Hi : 0000000000000000
> [ 0.000000] Lo : 0000000000000000
> [ 0.000000] epc : ffffffff81afada8 init_idle+0x130/0x270
> [ 0.000000] ra : ffffffff81afad90 init_idle+0x118/0x270
> [ 0.000000] Status: 540000e2 KX SX UX KERNEL EXL
> [ 0.000000] Cause : 00000008 (ExcCode 02)
> [ 0.000000] BadVA : 0000000000000000
> [ 0.000000] PrId : 00006305 (ICT Loongson-3)
> [ 0.000000] Process swapper (pid: 0, threadinfo=(____ptrval____), task=(____ptrval____), tls=0000000000000000)
> [ 0.000000] Stack : 9800000005dfbf00 ffffffff8178e950 0000000000000000 0000000000000000
> [ 0.000000] 0000000000000000 ffffffff81970000 000000000000003f ffffffff810a6528
> [ 0.000000] 0000000000000001 9800000005dfbe80 9800000005dfbf00 ffffffff81980000
> [ 0.000000] ffffffff810a6450 ffffffff81afb6c0 0000000000000000 ffffffff810a2258
> [ 0.000000] ffffffff81d82ec8 ffffffff8198d010 ffffffff81b67e80 ffffffff8197dd98
> [ 0.000000] ffffffff81d81c80 ffffffff81930000 0000000000000040 0000000000000000
> [ 0.000000] 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> [ 0.000000] 0000000000000000 000000000000009e ffffffff9fc01000 0000000000000000
> [ 0.000000] 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> [ 0.000000] 0000000000000000 ffffffff81ae86dc ffffffff81b3c741 0000000000000002
> [ 0.000000] ...
> [ 0.000000] Call Trace:
> [ 0.000000] [<ffffffff81afada8>] init_idle+0x130/0x270
> [ 0.000000] [<ffffffff81afb6c0>] sched_init+0x5c8/0x6c0
> [ 0.000000] [<ffffffff81ae86dc>] start_kernel+0x27c/0x7a8
>
> This bug has been reported to LLVM[2] and affects version from (at
> least) 18 to 21. Let's work around this by using inline assembly to
> assign $gp before a fix is widely available.
>
> Cc: stable@vger.kernel.org
> Link: https://gcc.gnu.org/onlinedocs/gcc-15.2.0/gcc/Global-Register-Variables.html # [1]
> Link: https://github.com/llvm/llvm-project/issues/176546 # [2]
> Signed-off-by: Yao Zi <me@ziyao.cc>
Gently ping on this patch. Thanks for your time and review.
Regards,
Yao Zi
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] MIPS: Work around LLVM bug when gp is used as global register variable
2026-01-18 9:02 [PATCH] MIPS: Work around LLVM bug when gp is used as global register variable Yao Zi
2026-02-02 15:07 ` Yao Zi
@ 2026-02-02 23:23 ` Nathan Chancellor
2026-02-03 4:03 ` Yao Zi
1 sibling, 1 reply; 4+ messages in thread
From: Nathan Chancellor @ 2026-02-02 23:23 UTC (permalink / raw)
To: Yao Zi
Cc: Thomas Bogendoerfer, Nick Desaulniers, Bill Wendling,
Justin Stitt, Thomas Weißschuh, linux-mips, linux-kernel,
llvm, stable
On Sun, Jan 18, 2026 at 09:02:35AM +0000, Yao Zi wrote:
> On MIPS, __current_thread_info is defined as global register variable
> locating in $gp, and is simply assigned with new address during kernel
> relocation.
>
> This however is broken with LLVM, which always restores $gp if it finds
> $gp is clobbered in any form, including when intentionally through a
> global register variable. This is against GCC's documentation[1], which
> requires a callee-saved register used as global register variable not to
> be restored if it's clobbered.
>
> As a result, $gp will continue to point to the unrelocated kernel after
> the epilog of relocate_kernel(), leading to an early crash in init_idle,
>
> [ 0.000000] CPU 0 Unable to handle kernel paging request at virtual address 0000000000000000, epc == ffffffff81afada8, ra == ffffffff81afad90
> [ 0.000000] Oops[#1]:
> [ 0.000000] CPU: 0 UID: 0 PID: 0 Comm: swapper Tainted: G W 6.19.0-rc5-00262-gd3eeb99bbc99-dirty #188 VOLUNTARY
> [ 0.000000] Tainted: [W]=WARN
> [ 0.000000] Hardware name: loongson,loongson64v-4core-virtio
> [ 0.000000] $ 0 : 0000000000000000 0000000000000000 0000000000000001 0000000000000000
> [ 0.000000] $ 4 : ffffffff80b80ec0 ffffffff80b53d48 0000000000000000 00000000000f4240
> [ 0.000000] $ 8 : 0000000000000100 ffffffff81d82f80 ffffffff81d82f80 0000000000000001
> [ 0.000000] $12 : 0000000000000000 ffffffff81776f58 00000000000005da 0000000000000002
> [ 0.000000] $16 : ffffffff80b80e40 0000000000000000 ffffffff80b81614 9800000005dfbe80
> [ 0.000000] $20 : 00000000540000e0 ffffffff81980000 0000000000000000 ffffffff80f81c80
> [ 0.000000] $24 : 0000000000000a26 ffffffff8114fb90
> [ 0.000000] $28 : ffffffff80b50000 ffffffff80b53d40 0000000000000000 ffffffff81afad90
> [ 0.000000] Hi : 0000000000000000
> [ 0.000000] Lo : 0000000000000000
> [ 0.000000] epc : ffffffff81afada8 init_idle+0x130/0x270
> [ 0.000000] ra : ffffffff81afad90 init_idle+0x118/0x270
> [ 0.000000] Status: 540000e2 KX SX UX KERNEL EXL
> [ 0.000000] Cause : 00000008 (ExcCode 02)
> [ 0.000000] BadVA : 0000000000000000
> [ 0.000000] PrId : 00006305 (ICT Loongson-3)
> [ 0.000000] Process swapper (pid: 0, threadinfo=(____ptrval____), task=(____ptrval____), tls=0000000000000000)
> [ 0.000000] Stack : 9800000005dfbf00 ffffffff8178e950 0000000000000000 0000000000000000
> [ 0.000000] 0000000000000000 ffffffff81970000 000000000000003f ffffffff810a6528
> [ 0.000000] 0000000000000001 9800000005dfbe80 9800000005dfbf00 ffffffff81980000
> [ 0.000000] ffffffff810a6450 ffffffff81afb6c0 0000000000000000 ffffffff810a2258
> [ 0.000000] ffffffff81d82ec8 ffffffff8198d010 ffffffff81b67e80 ffffffff8197dd98
> [ 0.000000] ffffffff81d81c80 ffffffff81930000 0000000000000040 0000000000000000
> [ 0.000000] 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> [ 0.000000] 0000000000000000 000000000000009e ffffffff9fc01000 0000000000000000
> [ 0.000000] 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> [ 0.000000] 0000000000000000 ffffffff81ae86dc ffffffff81b3c741 0000000000000002
> [ 0.000000] ...
> [ 0.000000] Call Trace:
> [ 0.000000] [<ffffffff81afada8>] init_idle+0x130/0x270
> [ 0.000000] [<ffffffff81afb6c0>] sched_init+0x5c8/0x6c0
> [ 0.000000] [<ffffffff81ae86dc>] start_kernel+0x27c/0x7a8
>
> This bug has been reported to LLVM[2] and affects version from (at
> least) 18 to 21. Let's work around this by using inline assembly to
> assign $gp before a fix is widely available.
>
> Cc: stable@vger.kernel.org
> Link: https://gcc.gnu.org/onlinedocs/gcc-15.2.0/gcc/Global-Register-Variables.html # [1]
> Link: https://github.com/llvm/llvm-project/issues/176546 # [2]
> Signed-off-by: Yao Zi <me@ziyao.cc>
Acked-by: Nathan Chancellor <nathan@kernel.org>
Hopefully the MIPS LLVM folks can look into this (even though I think
the MIPS backend is one of the less maintained backends in LLVM).
> ---
> arch/mips/kernel/relocate.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/arch/mips/kernel/relocate.c b/arch/mips/kernel/relocate.c
> index 7f1c136ad850..12aa0bbdd65e 100644
> --- a/arch/mips/kernel/relocate.c
> +++ b/arch/mips/kernel/relocate.c
> @@ -420,7 +420,18 @@ void *__init relocate_kernel(void)
> goto out;
>
> /* The current thread is now within the relocated image */
> +#ifndef CONFIG_CC_IS_CLANG
I find
#ifdef FOO
<FOO block>
#else
<!FOO block>
#endif
to be easier to read and process
#ifndef FOO
<!FOO block>
#else
<FOO block>
#endif
but maybe that it is just personal preference.
> __current_thread_info = RELOCATED(&init_thread_union);
> +#else
> + /*
> + * LLVM may wrongly restore $gp ($28) in epilog even if it's
> + * intentionally modified. Work around this by using inline
> + * assembly to assign $gp. $gp couldn't be listed as output or
> + * clobber, or LLVM will still restore its original value.
This comment should likely include a link to the LLVM upstream report to
make it easier to version restrict this workaround when fixed in the
future.
> + */
> + asm volatile("move $28, %0" : :
> + "r" (RELOCATED(&init_thread_union)));
> +#endif
>
> /* Return the new kernel's entry point */
> kernel_entry = RELOCATED(start_kernel);
> --
> 2.52.0
>
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] MIPS: Work around LLVM bug when gp is used as global register variable
2026-02-02 23:23 ` Nathan Chancellor
@ 2026-02-03 4:03 ` Yao Zi
0 siblings, 0 replies; 4+ messages in thread
From: Yao Zi @ 2026-02-03 4:03 UTC (permalink / raw)
To: Nathan Chancellor
Cc: Thomas Bogendoerfer, Nick Desaulniers, Bill Wendling,
Justin Stitt, Thomas Weißschuh, linux-mips, linux-kernel,
llvm, stable
On Mon, Feb 02, 2026 at 04:23:09PM -0700, Nathan Chancellor wrote:
> On Sun, Jan 18, 2026 at 09:02:35AM +0000, Yao Zi wrote:
> > On MIPS, __current_thread_info is defined as global register variable
> > locating in $gp, and is simply assigned with new address during kernel
> > relocation.
> >
> > This however is broken with LLVM, which always restores $gp if it finds
> > $gp is clobbered in any form, including when intentionally through a
> > global register variable. This is against GCC's documentation[1], which
> > requires a callee-saved register used as global register variable not to
> > be restored if it's clobbered.
> >
> > As a result, $gp will continue to point to the unrelocated kernel after
> > the epilog of relocate_kernel(), leading to an early crash in init_idle,
> >
> > [ 0.000000] CPU 0 Unable to handle kernel paging request at virtual address 0000000000000000, epc == ffffffff81afada8, ra == ffffffff81afad90
> > [ 0.000000] Oops[#1]:
> > [ 0.000000] CPU: 0 UID: 0 PID: 0 Comm: swapper Tainted: G W 6.19.0-rc5-00262-gd3eeb99bbc99-dirty #188 VOLUNTARY
> > [ 0.000000] Tainted: [W]=WARN
> > [ 0.000000] Hardware name: loongson,loongson64v-4core-virtio
> > [ 0.000000] $ 0 : 0000000000000000 0000000000000000 0000000000000001 0000000000000000
> > [ 0.000000] $ 4 : ffffffff80b80ec0 ffffffff80b53d48 0000000000000000 00000000000f4240
> > [ 0.000000] $ 8 : 0000000000000100 ffffffff81d82f80 ffffffff81d82f80 0000000000000001
> > [ 0.000000] $12 : 0000000000000000 ffffffff81776f58 00000000000005da 0000000000000002
> > [ 0.000000] $16 : ffffffff80b80e40 0000000000000000 ffffffff80b81614 9800000005dfbe80
> > [ 0.000000] $20 : 00000000540000e0 ffffffff81980000 0000000000000000 ffffffff80f81c80
> > [ 0.000000] $24 : 0000000000000a26 ffffffff8114fb90
> > [ 0.000000] $28 : ffffffff80b50000 ffffffff80b53d40 0000000000000000 ffffffff81afad90
> > [ 0.000000] Hi : 0000000000000000
> > [ 0.000000] Lo : 0000000000000000
> > [ 0.000000] epc : ffffffff81afada8 init_idle+0x130/0x270
> > [ 0.000000] ra : ffffffff81afad90 init_idle+0x118/0x270
> > [ 0.000000] Status: 540000e2 KX SX UX KERNEL EXL
> > [ 0.000000] Cause : 00000008 (ExcCode 02)
> > [ 0.000000] BadVA : 0000000000000000
> > [ 0.000000] PrId : 00006305 (ICT Loongson-3)
> > [ 0.000000] Process swapper (pid: 0, threadinfo=(____ptrval____), task=(____ptrval____), tls=0000000000000000)
> > [ 0.000000] Stack : 9800000005dfbf00 ffffffff8178e950 0000000000000000 0000000000000000
> > [ 0.000000] 0000000000000000 ffffffff81970000 000000000000003f ffffffff810a6528
> > [ 0.000000] 0000000000000001 9800000005dfbe80 9800000005dfbf00 ffffffff81980000
> > [ 0.000000] ffffffff810a6450 ffffffff81afb6c0 0000000000000000 ffffffff810a2258
> > [ 0.000000] ffffffff81d82ec8 ffffffff8198d010 ffffffff81b67e80 ffffffff8197dd98
> > [ 0.000000] ffffffff81d81c80 ffffffff81930000 0000000000000040 0000000000000000
> > [ 0.000000] 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> > [ 0.000000] 0000000000000000 000000000000009e ffffffff9fc01000 0000000000000000
> > [ 0.000000] 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> > [ 0.000000] 0000000000000000 ffffffff81ae86dc ffffffff81b3c741 0000000000000002
> > [ 0.000000] ...
> > [ 0.000000] Call Trace:
> > [ 0.000000] [<ffffffff81afada8>] init_idle+0x130/0x270
> > [ 0.000000] [<ffffffff81afb6c0>] sched_init+0x5c8/0x6c0
> > [ 0.000000] [<ffffffff81ae86dc>] start_kernel+0x27c/0x7a8
> >
> > This bug has been reported to LLVM[2] and affects version from (at
> > least) 18 to 21. Let's work around this by using inline assembly to
> > assign $gp before a fix is widely available.
> >
> > Cc: stable@vger.kernel.org
> > Link: https://gcc.gnu.org/onlinedocs/gcc-15.2.0/gcc/Global-Register-Variables.html # [1]
> > Link: https://github.com/llvm/llvm-project/issues/176546 # [2]
> > Signed-off-by: Yao Zi <me@ziyao.cc>
>
> Acked-by: Nathan Chancellor <nathan@kernel.org>
>
> Hopefully the MIPS LLVM folks can look into this (even though I think
> the MIPS backend is one of the less maintained backends in LLVM).
Sigh...
> > ---
> > arch/mips/kernel/relocate.c | 11 +++++++++++
> > 1 file changed, 11 insertions(+)
> >
> > diff --git a/arch/mips/kernel/relocate.c b/arch/mips/kernel/relocate.c
> > index 7f1c136ad850..12aa0bbdd65e 100644
> > --- a/arch/mips/kernel/relocate.c
> > +++ b/arch/mips/kernel/relocate.c
> > @@ -420,7 +420,18 @@ void *__init relocate_kernel(void)
> > goto out;
> >
> > /* The current thread is now within the relocated image */
> > +#ifndef CONFIG_CC_IS_CLANG
>
> I find
>
> #ifdef FOO
> <FOO block>
> #else
> <!FOO block>
> #endif
>
> to be easier to read and process
>
> #ifndef FOO
> <!FOO block>
> #else
> <FOO block>
> #endif
>
> but maybe that it is just personal preference.
I preferred to put Clang's workaround later, since
> > __current_thread_info = RELOCATED(&init_thread_union);
this simple assignment is easier to read and more clear than the inline
assembly, and matching the comment
/* The current thread is now within the relocated image */
better. But yes, this is basically a personal preference, and I'm happy
with both. Please tell me if you do prefer the other.
> > +#else
> > + /*
> > + * LLVM may wrongly restore $gp ($28) in epilog even if it's
> > + * intentionally modified. Work around this by using inline
> > + * assembly to assign $gp. $gp couldn't be listed as output or
> > + * clobber, or LLVM will still restore its original value.
>
> This comment should likely include a link to the LLVM upstream report to
> make it easier to version restrict this workaround when fixed in the
> future.
Sure, will do it in v2. Thanks for the feedback!
Best regards,
Yao Zi
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2026-02-03 4:04 UTC | newest]
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2026-01-18 9:02 [PATCH] MIPS: Work around LLVM bug when gp is used as global register variable Yao Zi
2026-02-02 15:07 ` Yao Zi
2026-02-02 23:23 ` Nathan Chancellor
2026-02-03 4:03 ` Yao Zi
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