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Re: [patch] getauxval.3 correct AT_HWCAP result description


Hello James,

On 07/12/2016 06:35 PM, Cownie, James H wrote:
The getauxval(3) man page describes the result for AT_HWCAP as "A
pointer to a multibyte mask of bits", however the actual value
returned is not a pointer, but simply the first 32 bits of the
capabilities mask.

This can be observed directly. Note the value shown for AT_HWCAP is a
32 bit value that is not a pointer (see AT_PHDR or AT_RANDOM for how
pointers are shown).

Thanks! Patch applied.

Cheers,

Michael


% LD_SHOW_AUXV=1 cat < /dev/null
AT_SYSINFO_EHDR: 0x7fffe89fe000
AT_HWCAP:        bfebfbff
AT_PAGESZ:       4096
AT_CLKTCK:       100
AT_PHDR:         0x400040
AT_PHENT:        56
AT_PHNUM:        9
AT_BASE:         0x0
AT_FLAGS:        0x0
AT_ENTRY:        0x402634
AT_UID:          515
AT_EUID:         515
AT_GID:          114
AT_EGID:         114
AT_SECURE:       0
AT_RANDOM:       0x7fffe8917be9
AT_EXECFN:       /usr/bin/cat
AT_PLATFORM:     x86_64


--- PATCH ---
diff --git a/man3/getauxval.3 b/man3/getauxval.3
index 85d7f41..7ce0237 100644
--- a/man3/getauxval.3
+++ b/man3/getauxval.3
@@ -101,12 +101,13 @@ performed by the kernel.
 The real group ID of the thread.
 .TP
 .BR AT_HWCAP
-A pointer to a multibyte mask of bits whose settings
+A four byte long bit-mask whose settings
 indicate detailed processor capabilities.
 The contents of the bit mask are hardware dependent
 (for example, see the kernel source file
 .IR arch/x86/include/asm/cpufeature.h
-for details relating to the Intel x86 architecture).
+for details relating to the Intel x86 architecture; the value
+returned is the first 32 bit word of the array described there).
 A human-readable version of the same information is available via
 .IR /proc/cpuinfo .
 .TP
--- END PATCH ---

-- Jim

James Cownie <james.h.cownie@intel.com>
SSG/DPD/TCAR (Technical Computing, Analyzers and Runtimes)
Tel: +44 117 9071438


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--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/


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