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// SPDX-License-Identifier: GPL-2.0
/*
* Two constructs which appear all over the kernel and must not upset klp
* checksum or klp diff.
*
* An absolute symbol (SHN_ABS) has no section, so anything walking sym->sec
* without checking dereferences NULL. The kernel makes them with linker
* scripts and with .set in asm; VDSO and the fixed-address per-cpu bases are
* the usual sources.
*
* __ADDRESSABLE() emits a pointer into .discard.addressable purely to keep a
* symbol referenced. It is discarded at link time and means nothing to a
* livepatch, but the pointer is a relocation like any other and has to survive
* being looked at.
*
* Neither is the subject of the patch; the point is that their presence does
* not disturb the function that is.
*/
static const char __modinfo[]
__attribute__((section(".modinfo"), used, aligned(1))) = "\0name=vmlinux";
/* SHN_ABS, referenced from code. */
extern char abs_sym[];
__asm__(".globl abs_sym\n"
".set abs_sym, 0x1234\n");
int helper(int x);
int helper(int x) { return x + 1; }
/* The shape of __ADDRESSABLE(helper). */
__asm__(".pushsection .discard.addressable, \"aw\"\n"
".balign 8\n"
".quad helper\n"
".popsection\n");
int target(int x)
{
#ifdef PATCHED
return helper(x) + (int)(long)abs_sym + 1;
#else
return helper(x) + (int)(long)abs_sym;
#endif
}
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