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// SPDX-License-Identifier: GPL-2.0
/*
* An x86 alternative whose replacement instruction carries a text annotation.
*
* The kernel does this wherever an ALTERNATIVE contains something objtool has
* to be told about -- a retpoline-safe indirect branch, an intentionally
* missing ENDBR -- so the .discard.annotate_insn entry references an address
* inside .altinstr_replacement rather than inside a function.
*
* Two things make that awkward for klp diff, and both are why this fixture
* exists. Replacement code has no real symbol: objtool invents a NOTYPE fake
* symbol for it, so an annotation pointing there does not reference a FUNC.
* And .discard.annotate_insn has to be cloned after .altinstructions, or the
* replacement it names has no clone to point at yet.
*
* struct alt_instr is written out by hand as in empty_alternative.c: s32
* instr_offset, s32 repl_offset, u32 ft_flags, u8 instrlen, u8 replacementlen,
* with an entsize so klp diff can find the entry boundaries.
* .discard.annotate_insn entries are s32 offset, s32 type; type 2 is
* ANNOTYPE_RETPOLINE_SAFE.
*
* The replacement label is global so the relocations name it rather than
* .altinstr_replacement plus an addend, which klp diff cannot convert. It is
* still NOTYPE, which is the shape that matters here.
*/
static const char __modinfo[]
__attribute__((section(".modinfo"), used, aligned(1))) = "\0name=vmlinux";
int target(int x)
{
asm volatile(
"661: nop\n\t"
".pushsection .altinstr_replacement, \"ax\"\n\t"
".globl target_repl\n\t"
"target_repl:\n\t"
" nop\n\t"
/* The annotation lands inside the replacement. */
".pushsection .discard.annotate_insn, \"M\", @progbits, 8\n\t"
".long target_repl - .\n\t"
".long 2\n\t"
".popsection\n\t"
"target_repl_end:\n\t"
".popsection\n\t"
".pushsection .altinstructions, \"aM\", @progbits, 14\n\t"
".long 661b - .\n\t"
".long target_repl - .\n\t"
".long 0\n\t"
".byte 1\n\t"
".byte target_repl_end - target_repl\n\t"
".popsection\n\t");
#ifdef PATCHED
return x + 2;
#else
return x + 1;
#endif
}
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