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RISC-V: Fix IFUNC resolver cannot access gp pointer

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In some cases, an IFUNC resolver may need to access the gp pointer to
access global variables. Such an object may have l_relocated == 0 at
this time. In this case, an IFUNC resolver will fail to access a global
variable and cause a SIGSEGV.

This patch fixes this issue by relaxing the check of l_relocated in
elf_machine_runtime_setup, but added a check for SHARED case to avoid
using this code in static-linked executables. Such object have already
set up the gp pointer in load_gp function and l->l_scope will be NULL if
it is a pie object. So if we use these code to set up the gp pointer
again for static-pie, it will causing a SIGSEGV in glibc as original bug
on BZ #31317.

I have also reproduced and checked BZ #31317 using the mold commit
bed5b1731b ("illumos: Treat absolute symbols specially"), this patch can
fix the issue.

Also, we used the wrong gp pointer previously because ref->st_value is
not the relocated address but just the offset from the base address of
ELF. An edge case may happen if we reference gp pointer in a IFUNC
resolver in a PIE object, but it will not happen in compiler-generated
codes since -pie will disable relax to gp. In this case, the GP will be
initialized incorrectly since the ref->st_value is not the address after
relocation. This patch fixes this issue by adding the l->l_addr to
ref->st_value to get the relocated address for the gp pointer. We don't
use SYMBOL_ADDRESS macro here because __global_pointer$ is a special
symbol that has SHN_ABS type, but it will use PC-relative addressing in
the load_gp function using lla.

Closes: BZ #32269
Fixes: 96d1b9ac23 ("RISC-V: Fix the static-PIE non-relocated object check")

Co-authored-by: Vivian Wang <dramforever@live.com>
Signed-off-by: Yangyu Chen <cyy@cyyself.name>
This commit is contained in:
Yangyu Chen 2025-02-25 01:12:19 +08:00 • committed by Andreas Schwab
parent 935563754b
commit 3fd2ff7685
1 changed files with 11 additions and 6 deletions
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17
sysdeps/riscv/dl-machine.h
View file

@ -348,7 +348,8 @@ elf_machine_runtime_setup (struct link_map *l, struct r_scope_elem *scope[],
gotplt[1] = (ElfW(Addr)) l; gotplt[1] = (ElfW(Addr)) l;
} }
if (l->l_type == lt_executable && l->l_relocated) #ifdef SHARED
if (l->l_type == lt_executable)
{ {
/* The __global_pointer$ may not be defined by the linker if the /* The __global_pointer$ may not be defined by the linker if the
$gp register does not be used to access the global variable $gp register does not be used to access the global variable
@ -362,12 +363,16 @@ elf_machine_runtime_setup (struct link_map *l, struct r_scope_elem *scope[],
_dl_lookup_symbol_x ("__global_pointer$", l, &ref, _dl_lookup_symbol_x ("__global_pointer$", l, &ref,
l->l_scope, NULL, 0, 0, NULL); l->l_scope, NULL, 0, 0, NULL);
if (ref) if (ref)
asm ( asm (
"mv gp, %0\n" "mv gp, %0\n"
: :
: "r" (ref->st_value) : "r" (ref->st_value + l->l_addr)
); /* Don't use SYMBOL_ADDRESS here since __global_pointer$
can be SHN_ABS type, but we need the address relative to
PC, not the absolute address. */
);
} }
#endif
#endif #endif
return lazy; return lazy;
} }