Messages in this thread | | | Date | Thu, 7 Feb 2019 13:17:29 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH v6 02/27] x86: Use symbol name in jump table for PIE support |
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On Thu, Jan 31, 2019 at 11:24:09AM -0800, Thomas Garnier wrote: > Replace the %c constraint with %P. The %c is incompatible with PIE > because it implies an immediate value whereas %P reference a symbol.
How so?
AFAIK, %c requires a constant operand and if %P is used to print a constant, it simply drops syntax-specific prefixes and does a bare constant.
I guess that here
https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#x86Operandmodifiers
is not entirely correct as it should not say "If used for a constant" for %P but say "symbol or constant".
But before/after asm doesn't show any difference. So what gives?
before: # 39 "./arch/x86/include/asm/jump_label.h" 1 1: .byte 0xe9 .long .L241 - 2f # 2: .pushsection __jump_table, "aw" .balign 8 .long 1b - ., .L241 - . # .quad __use_tsc + 1 - . #, .popsection
after: # 39 "./arch/x86/include/asm/jump_label.h" 1 1: .byte 0xe9 .long .L241 - 2f # 2: .pushsection __jump_table, "aw" .balign 8 .long 1b - ., .L241 - . # .quad __use_tsc+1 - . # .popsection
-- Regards/Gruss, Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
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