[Buildroot] [PATCH v5] Config.in: ban textrels on musl toolchains

[Buildroot] [PATCH v5] Config.in: ban textrels on musl toolchains

[J. Neuschäfer via buildroot]

musl-libc doesn't support TEXTRELs[1] and programs with TEXTRELs will
crash on start-up under musl.

This patch forbids the use of TEXTRELs on musl toolchains with dynamic
linking.

To verify this patch:

- Delete package/micropython/0001-py-nlrthumb-Make-non-Thumb2-long-jump-workaround-opt.patch
- Build micropython (before v1.23) with a musl toolchain and
  BR2_SHARED_LIBS. The build should abort while linking micropython.

[1]: https://www.openwall.com/lists/musl/2020/09/25/4

Signed-off-by: J. Neuschäfer <j.neuschaefer@gmx.net>
---
Changes in v5:
- Fix boolean logic (ifeq...)
- Link to v4: https://lore.kernel.org/r/20240718-ztext-v4-1-15a9744f1edb@gmx.net

Changes in v4:
- Remove Config.in option, implement the whole logic in
  package/Makefile.in
- Document how to verify
- Link to v3: https://lore.kernel.org/r/20240704-ztext-v3-1-9195d06c8bd0@gmx.net

Changes in v3:
- drop micropython patch (already merged)
- rewrite to positive logic, as suggested by Yann E. MORIN
- Link to v2: https://lore.kernel.org/r/20240529-ztext-v2-0-82985032f169@gmx.net

Changes in v2:
- Slightly different wording
- Enable the option by default on musl toolchains
- Add patch to fix build of micropython

Link to v1:
- https://lore.kernel.org/r/20240419-ztext-v1-1-a8d5c2cfcf57@gmx.net
---
---
 package/Makefile.in | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/package/Makefile.in b/package/Makefile.in
index 47a89f1ae1..1cedfefa7e 100644
--- a/package/Makefile.in
+++ b/package/Makefile.in
@@ -149,6 +149,15 @@ endif

 TARGET_LDFLAGS = $(call qstrip,$(BR2_TARGET_LDFLAGS))

+# musl's dynamic loader doesn't support DT_TEXTREL, which results in a runtime
+# crash if it gets used. The "-z text" linker option issues a build-time error
+# when DT_TEXREL is used, so we capture the problem earlier.
+#
+# See also: https://www.openwall.com/lists/musl/2020/09/25/4
+ifeq ($(BR2_TOOLCHAIN_USES_MUSL):$(BR2_STATIC_LIBS),y:)
+TARGET_LDFLAGS += -Wl,-z,text
+endif
+
 # By design, _FORTIFY_SOURCE requires gcc optimization to be enabled.
 # Therefore, we need to pass _FORTIFY_SOURCE and the optimization level
 # through the same mechanism, i.e currently through CFLAGS. Passing

---
base-commit: 89e3b2fb846506217b4767fe9165f1641a407314
change-id: 20240417-ztext-5accbab61c0a

Best regards,
--
J. Neuschäfer <j.neuschaefer@gmx.net>

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Re: [Buildroot] [PATCH v5] Config.in: ban textrels on musl toolchains

[Thomas Petazzoni via buildroot]

Hello J,

On Fri, 19 Jul 2024 17:27:19 +0200
J. Neuschäfer via buildroot <buildroot@buildroot.org> wrote:

> musl-libc doesn't support TEXTRELs[1] and programs with TEXTRELs will
> crash on start-up under musl.
> 
> This patch forbids the use of TEXTRELs on musl toolchains with dynamic
> linking.
> 
> To verify this patch:
> 
> - Delete package/micropython/0001-py-nlrthumb-Make-non-Thumb2-long-jump-workaround-opt.patch
> - Build micropython (before v1.23) with a musl toolchain and
>   BR2_SHARED_LIBS. The build should abort while linking micropython.
> 
> [1]: https://www.openwall.com/lists/musl/2020/09/25/4
> 
> Signed-off-by: J. Neuschäfer <j.neuschaefer@gmx.net>
> ---
> Changes in v5:
> - Fix boolean logic (ifeq...)
> - Link to v4: https://lore.kernel.org/r/20240718-ztext-v4-1-15a9744f1edb@gmx.net

Applied to master, thanks. If you could
monitor http://autobuild.buildroot.net/?libc=musl in the next
few days to check for any issue related to this change, it would be
nice. Thanks!

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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Re: [Buildroot] [PATCH v5] Config.in: ban textrels on musl toolchains

[Thomas Petazzoni via buildroot]

Hello J,

On Fri, 19 Jul 2024 17:27:19 +0200
J. Neuschäfer via buildroot <buildroot@buildroot.org> wrote:

> +# See also: https://www.openwall.com/lists/musl/2020/09/25/4
> +ifeq ($(BR2_TOOLCHAIN_USES_MUSL):$(BR2_STATIC_LIBS),y:)
> +TARGET_LDFLAGS += -Wl,-z,text
> +endif

Unfortunately, this change is breaking the build of gnu-efi:

  http://autobuild.buildroot.net/results/e3d/e3dec7e0323a3fcb07269b3f9e73becaafeedecd/build-end.log

It seems like gnu-efi uses $(TARGET_LDFLAGS) directly as arguments to
the linker, not as arguments to gcc-used-as-a-linker, and the linker
doesn't know about -Wl,-z,-text.

So, either we to "-z text" which I believe is understood by both gcc
and ld, or we somehow fix gnu-efi.

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com
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Re: [Buildroot] [PATCH v5] Config.in: ban textrels on musl toolchains

[J. Neuschäfer via buildroot]

On Wed, Jul 31, 2024 at 12:03:59AM +0200, Thomas Petazzoni wrote:
> Hello J,
>
> On Fri, 19 Jul 2024 17:27:19 +0200
> J. Neuschäfer via buildroot <buildroot@buildroot.org> wrote:
>
> > +# See also: https://www.openwall.com/lists/musl/2020/09/25/4
> > +ifeq ($(BR2_TOOLCHAIN_USES_MUSL):$(BR2_STATIC_LIBS),y:)
> > +TARGET_LDFLAGS += -Wl,-z,text
> > +endif
>
> Unfortunately, this change is breaking the build of gnu-efi:
>
>   http://autobuild.buildroot.net/results/e3d/e3dec7e0323a3fcb07269b3f9e73becaafeedecd/build-end.log
>
> It seems like gnu-efi uses $(TARGET_LDFLAGS) directly as arguments to
> the linker, not as arguments to gcc-used-as-a-linker, and the linker
> doesn't know about -Wl,-z,-text.

Hm, this is an interesting case, because AFAIU gnu-efi is a bare-metal
library (more or less), so it won't be using the musl ld.so anyway.
So it would be completely reasonable to strip out the -z text here.

> So, either we to "-z text" which I believe is understood by both gcc
> and ld, or we somehow fix gnu-efi.

I think I prefer the first option (with an explanatory comment). I'll
send a patch when I get around to it.


-- jn
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Re: [Buildroot] [PATCH v5] Config.in: ban textrels on musl toolchains

[yann.morin]

J., All,

+Bernd and +David for x264:

On 2024-07-19 17:27 +0200, J. Neuschäfer via buildroot spake thusly:
> This patch forbids the use of TEXTRELs on musl toolchains with dynamic
> linking.

Another build failure due to this change:

    [...]/buildroot/output/per-package/x264/host/bin/../lib/gcc/i586-buildroot-linux-musl/12.4.0/../../../../i586-buildroot-linux-musl/bin/ld: common/x86/dct-a-8.o: warning: relocation in read-only section `.text'
    [...]/buildroot/output/per-package/x264/host/bin/i586-buildroot-linux-musl-gcc-ranlib libx264.a
    [...]/buildroot/output/per-package/x264/host/bin/../lib/gcc/i586-buildroot-linux-musl/12.4.0/../../../../i586-buildroot-linux-musl/bin/ld: read-only segment has dynamic relocations
    collect2: error: ld returned 1 exit status
    make[2]: *** [Makefile:251: libx264.so.164] Error 1
    make[2]: *** Waiting for unfinished jobs....
    make[1]: *** [package/pkg-generic.mk:289: [...]/buildroot/output/build/x264-baee400fa9ced6f5481a728138fed6e867b0ff7f/.stamp_built] Error 2
    make: *** [Makefile:83: _all] Error 2

There is still no failure in the autobuilders, as x264 is quite late
in the alphabetical order, so it probably is just hidden by earlier
failures...

I have no idea what to look for to avoid those relocations in the first
place, so could you have a look, please?

Regards,
Yann E. MORIN.

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Re: [Buildroot] [PATCH v5] Config.in: ban textrels on musl toolchains

[J. Neuschäfer via buildroot]

On Tue, Aug 13, 2024 at 11:09:02AM +0200, yann.morin@orange.com wrote:
> J., All,
>
> +Bernd and +David for x264:
>
> On 2024-07-19 17:27 +0200, J. Neuschäfer via buildroot spake thusly:
> > This patch forbids the use of TEXTRELs on musl toolchains with dynamic
> > linking.
>
> Another build failure due to this change:
>
>     [...]/buildroot/output/per-package/x264/host/bin/../lib/gcc/i586-buildroot-linux-musl/12.4.0/../../../../i586-buildroot-linux-musl/bin/ld: common/x86/dct-a-8.o: warning: relocation in read-only section `.text'
>     [...]/buildroot/output/per-package/x264/host/bin/i586-buildroot-linux-musl-gcc-ranlib libx264.a
>     [...]/buildroot/output/per-package/x264/host/bin/../lib/gcc/i586-buildroot-linux-musl/12.4.0/../../../../i586-buildroot-linux-musl/bin/ld: read-only segment has dynamic relocations
>     collect2: error: ld returned 1 exit status
>     make[2]: *** [Makefile:251: libx264.so.164] Error 1
>     make[2]: *** Waiting for unfinished jobs....
>     make[1]: *** [package/pkg-generic.mk:289: [...]/buildroot/output/build/x264-baee400fa9ced6f5481a728138fed6e867b0ff7f/.stamp_built] Error 2
>     make: *** [Makefile:83: _all] Error 2
>
> There is still no failure in the autobuilders, as x264 is quite late
> in the alphabetical order, so it probably is just hidden by earlier
> failures...
>
> I have no idea what to look for to avoid those relocations in the first
> place, so could you have a look, please?

Hi Yann,

sorry for the delay, I was busy with other stuff for the past weeks.

I'll take a look at the libx264 textrel issue.


-- jn
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Re: [Buildroot] [PATCH v5] Config.in: ban textrels on musl toolchains

[J. Neuschäfer via buildroot]

On Tue, Aug 13, 2024 at 11:09:02AM +0200, yann.morin@orange.com wrote:
> J., All,
>
> +Bernd and +David for x264:
>
> On 2024-07-19 17:27 +0200, J. Neuschäfer via buildroot spake thusly:
> > This patch forbids the use of TEXTRELs on musl toolchains with dynamic
> > linking.
>
> Another build failure due to this change:
>
>     [...]/buildroot/output/per-package/x264/host/bin/../lib/gcc/i586-buildroot-linux-musl/12.4.0/../../../../i586-buildroot-linux-musl/bin/ld: common/x86/dct-a-8.o: warning: relocation in read-only section `.text'
>     [...]/buildroot/output/per-package/x264/host/bin/i586-buildroot-linux-musl-gcc-ranlib libx264.a
>     [...]/buildroot/output/per-package/x264/host/bin/../lib/gcc/i586-buildroot-linux-musl/12.4.0/../../../../i586-buildroot-linux-musl/bin/ld: read-only segment has dynamic relocations
>     collect2: error: ld returned 1 exit status
>     make[2]: *** [Makefile:251: libx264.so.164] Error 1
>     make[2]: *** Waiting for unfinished jobs....
>     make[1]: *** [package/pkg-generic.mk:289: [...]/buildroot/output/build/x264-baee400fa9ced6f5481a728138fed6e867b0ff7f/.stamp_built] Error 2
>     make: *** [Makefile:83: _all] Error 2
>
> There is still no failure in the autobuilders, as x264 is quite late
> in the alphabetical order, so it probably is just hidden by earlier
> failures...
>
> I have no idea what to look for to avoid those relocations in the first
> place, so could you have a look, please?
>
> Regards,
> Yann E. MORIN.

I took a look, the issue is that libx264's x86 assembly is position
dependent (patch coming in a separate email). For example:


SECTION .text

cextern pw_32
[...]

INIT_MMX mmx
cglobal add4x4_idct, 2,2
    pxor m7, m7
.skip_prologue:
    movq  m1, [r1+ 8]
    movq  m3, [r1+24]
    movq  m2, [r1+16]
    movq  m0, [r1+ 0]
    IDCT4_1D w,0,1,2,3,4,5
    TRANSPOSE4x4W 0,1,2,3,4
    paddw m0, [pw_32]           <--- here
    IDCT4_1D w,0,1,2,3,4,5
    STORE_DIFF  m0, m4, m7, [r0+0*FDEC_STRIDE]
    STORE_DIFF  m1, m4, m7, [r0+1*FDEC_STRIDE]
    STORE_DIFF  m2, m4, m7, [r0+2*FDEC_STRIDE]
    STORE_DIFF  m3, m4, m7, [r0+3*FDEC_STRIDE]
    RET


In my experience, hand-written assembly code is usually the culprit, but
of course not all hand-written assembly code has these issues.


-- jn
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