[PATCH] riscv: fix multi-letter extension compare

[PATCH] riscv: fix multi-letter extension compare

[Nikita Shubin]

From: Nikita Shubin <n.shubin@yadro.com>

Increment ext pointer to match letters after 'z' character, so it points
to actual extension name.

Fixes: 4905ec2fb7e6 ("RISC-V: Add sscofpmf extension support")
Signed-off-by: Nikita Shubin <n.shubin@yadro.com>
---
Hello Atish,

Sorry to blame you, but i double checked this and i don't see a way 
how extensions from device tree could be successfully matched with 
encoded ones without incrementing the ext pointer or prepending 
the encoded extensions with 'z' letter.

I have no idea how this could slip through review - am i missing something ?
---
 arch/riscv/kernel/cpufeature.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 3b5583db9d80..031546052dc0 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -199,6 +199,7 @@ void __init riscv_fill_hwcap(void)
 				this_hwcap |= isa2hwcap[(unsigned char)(*ext)];
 				set_bit(*ext - 'a', this_isa);
 			} else {
+				ext++;
 				SET_ISA_EXT_MAP("sscofpmf", RISCV_ISA_EXT_SSCOFPMF);
 				SET_ISA_EXT_MAP("svpbmt", RISCV_ISA_EXT_SVPBMT);
 				SET_ISA_EXT_MAP("zicbom", RISCV_ISA_EXT_ZICBOM);
-- 
2.35.1


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Re: [PATCH] riscv: fix multi-letter extension compare

[Jessica Clarke]

On 6 Oct 2022, at 08:02, Nikita Shubin <nikita.shubin@maquefel.me> wrote:
> 
> From: Nikita Shubin <n.shubin@yadro.com>
> 
> Increment ext pointer to match letters after 'z' character, so it points
> to actual extension name.
> 
> Fixes: 4905ec2fb7e6 ("RISC-V: Add sscofpmf extension support")
> Signed-off-by: Nikita Shubin <n.shubin@yadro.com>
> ---
> Hello Atish,
> 
> Sorry to blame you, but i double checked this and i don't see a way 
> how extensions from device tree could be successfully matched with 
> encoded ones without incrementing the ext pointer or prepending 
> the encoded extensions with 'z' letter.
> 
> I have no idea how this could slip through review - am i missing something ?
> ---
> arch/riscv/kernel/cpufeature.c | 1 +
> 1 file changed, 1 insertion(+)
> 
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 3b5583db9d80..031546052dc0 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -199,6 +199,7 @@ void __init riscv_fill_hwcap(void)
> 				this_hwcap |= isa2hwcap[(unsigned char)(*ext)];
> 				set_bit(*ext - 'a', this_isa);
> 			} else {
> +				ext++;
> 				SET_ISA_EXT_MAP("sscofpmf", RISCV_ISA_EXT_SSCOFPMF);
> 				SET_ISA_EXT_MAP("svpbmt", RISCV_ISA_EXT_SVPBMT);
> 				SET_ISA_EXT_MAP("zicbom", RISCV_ISA_EXT_ZICBOM);

This makes no sense. The single-letter prefix that’s part of the actual
extension name is already in the string there, whether s or z. Your
code means (a) you’d have to double up the prefix in the device tree
(which is obviously wrong) (b) you could use s or z interchangeably as
the first character (e.g. you’d make zzicbom and szicbom parsed as
zicbom).

Are you actually seeing a bug? Did you test this at all? This looks
like you misunderstood code and wrote an untested patch for a bug you
thought you saw.

Jess

> -- 
> 2.35.1
> 
> 
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Re: [PATCH] riscv: fix multi-letter extension compare

[Nikita Shubin]

Hello Atish,

My bad, i somehow decided that 'sscofpmf' should
be 'zsscofpmf' in device tree, but it's 'Sscofpmf' actually.

Sorry for noise please ignore this patch.

On Thu,  6 Oct 2022 10:02:56 +0300
Nikita Shubin <nikita.shubin@maquefel.me> wrote:

> From: Nikita Shubin <n.shubin@yadro.com>
> 
> Increment ext pointer to match letters after 'z' character, so it
> points to actual extension name.
> 
> Fixes: 4905ec2fb7e6 ("RISC-V: Add sscofpmf extension support")
> Signed-off-by: Nikita Shubin <n.shubin@yadro.com>
> ---
> Hello Atish,
> 
> Sorry to blame you, but i double checked this and i don't see a way 
> how extensions from device tree could be successfully matched with 
> encoded ones without incrementing the ext pointer or prepending 
> the encoded extensions with 'z' letter.
> 
> I have no idea how this could slip through review - am i missing
> something ? ---
>  arch/riscv/kernel/cpufeature.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/riscv/kernel/cpufeature.c
> b/arch/riscv/kernel/cpufeature.c index 3b5583db9d80..031546052dc0
> 100644 --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -199,6 +199,7 @@ void __init riscv_fill_hwcap(void)
>  				this_hwcap |= isa2hwcap[(unsigned
> char)(*ext)]; set_bit(*ext - 'a', this_isa);
>  			} else {
> +				ext++;
>  				SET_ISA_EXT_MAP("sscofpmf",
> RISCV_ISA_EXT_SSCOFPMF); SET_ISA_EXT_MAP("svpbmt",
> RISCV_ISA_EXT_SVPBMT); SET_ISA_EXT_MAP("zicbom",
> RISCV_ISA_EXT_ZICBOM);


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