[binutils-gdb] RISC-V: Go PLT for CALL/JUMP/RVC_JUMP if `h->plt.offset' isn't -1
Nelson Chu
nelsonc1225@sourceware.org
Fri Mar 7 03:04:28 GMT 2025
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=4295841be4392fcff33a1efee6d4345063021e6b
commit 4295841be4392fcff33a1efee6d4345063021e6b
Author: Nelson Chu <nelson@rivosinc.com>
Date: Sat Feb 8 16:33:37 2025 +0800
RISC-V: Go PLT for CALL/JUMP/RVC_JUMP if `h->plt.offset' isn't -1
I got an request about the undefined behaviors, considering the following case,
$ cat test.c
void main ()
{
foo();
}
$ cat lib.h
void foo(void);
$ riscv64-unknown-linux-gnu-gcc test.c
riscv64-unknown-linux-gnu/bin/ld: /tmp/ccRO8fJl.o: in function `main':
test.c:(.text+0x8): undefined reference to `foo'
collect2: error: ld returned 1 exit status
$ riscv64-unknown-linux-gnu-gcc test.c -Wl,--unresolved-symbols=ignore-in-object-files
$ qemu-riscv64 a.out
Segmentation fault (core dumped)
Testing with x86 and aarch64, they won't get the segfault since they go plt
for the undefined foo symbol. So, after applying this patch, I can get the
following too,
$ qemu-riscv64 a.out
a.out: symbol lookup error: a.out: undefined symbol: foo
The change of this patch should only affect the call behavior, which refer
to an undefined (weak) symbol, when building an dynamic executable. I think
the pic/pie behavior won't be affected as usual.
Diff:
---
bfd/elfnn-riscv.c | 84 +++++++++++++++++++++++++++++--------------------------
1 file changed, 44 insertions(+), 40 deletions(-)
diff --git a/bfd/elfnn-riscv.c b/bfd/elfnn-riscv.c
index 57ced95fdb3..bca3a585f56 100644
--- a/bfd/elfnn-riscv.c
+++ b/bfd/elfnn-riscv.c
@@ -2263,6 +2263,7 @@ riscv_elf_relocate_section (bfd *output_bfd,
reloc_howto_type *howto = riscv_elf_rtype_to_howto (input_bfd, r_type);
const char *msg = NULL;
bool resolved_to_zero;
+ bool via_plt = false;
if (howto == NULL)
continue;
@@ -2565,6 +2566,12 @@ riscv_elf_relocate_section (bfd *output_bfd,
resolved_to_zero = (h != NULL
&& UNDEFWEAK_NO_DYNAMIC_RELOC (info, h));
+ /* Refer to the PLT entry. This check has to match the check in
+ _bfd_riscv_relax_section. */
+ via_plt = (htab->elf.splt != NULL
+ && h != NULL
+ && h->plt.offset != MINUS_ONE);
+
switch (r_type)
{
case R_RISCV_NONE:
@@ -2776,8 +2783,7 @@ riscv_elf_relocate_section (bfd *output_bfd,
case R_RISCV_CALL_PLT:
/* Handle a call to an undefined weak function. This won't be
relaxed, so we have to handle it here. */
- if (h != NULL && h->root.type == bfd_link_hash_undefweak
- && (!bfd_link_pic (info) || h->plt.offset == MINUS_ONE))
+ if (h->root.type == bfd_link_hash_undefweak && !via_plt)
{
/* We can use x0 as the base register. */
bfd_vma insn = bfd_getl32 (contents + rel->r_offset + 4);
@@ -2791,42 +2797,40 @@ riscv_elf_relocate_section (bfd *output_bfd,
case R_RISCV_JAL:
case R_RISCV_RVC_JUMP:
- if (bfd_link_pic (info) && h != NULL)
+ if (via_plt)
{
- if (h->plt.offset != MINUS_ONE)
- {
- /* Refer to the PLT entry. This check has to match the
- check in _bfd_riscv_relax_section. */
- relocation = sec_addr (htab->elf.splt) + h->plt.offset;
- unresolved_reloc = false;
- }
- else if (!SYMBOL_REFERENCES_LOCAL (info, h)
- && (input_section->flags & SEC_ALLOC) != 0
- && (input_section->flags & SEC_READONLY) != 0
- && ELF_ST_VISIBILITY (h->other) == STV_DEFAULT)
- {
- /* PR 28509, when generating the shared object, these
- referenced symbols may bind externally, which means
- they will be exported to the dynamic symbol table,
- and are preemptible by default. These symbols cannot
- be referenced by the non-pic relocations, like
- R_RISCV_JAL and R_RISCV_RVC_JUMP relocations.
-
- However, consider that linker may relax the R_RISCV_CALL
- relocations to R_RISCV_JAL or R_RISCV_RVC_JUMP, if
- these relocations are relocated to the plt entries,
- then we won't report error for them.
-
- Perhaps we also need the similar checks for the
- R_RISCV_BRANCH and R_RISCV_RVC_BRANCH relocations. */
- msg = bfd_asprintf (_("%%X%%P: relocation %s against `%s'"
- " which may bind externally"
- " can not be used"
- " when making a shared object;"
- " recompile with -fPIC\n"),
- howto->name, h->root.root.string);
- r = bfd_reloc_notsupported;
- }
+ relocation = sec_addr (htab->elf.splt) + h->plt.offset;
+ unresolved_reloc = false;
+ }
+ else if (bfd_link_pic (info)
+ && h != NULL
+ && h->plt.offset == MINUS_ONE
+ && !SYMBOL_REFERENCES_LOCAL (info, h)
+ && (input_section->flags & SEC_ALLOC) != 0
+ && (input_section->flags & SEC_READONLY) != 0
+ && ELF_ST_VISIBILITY (h->other) == STV_DEFAULT)
+ {
+ /* PR 28509, when generating the shared object, these
+ referenced symbols may bind externally, which means
+ they will be exported to the dynamic symbol table,
+ and are preemptible by default. These symbols cannot
+ be referenced by the non-pic relocations, like
+ R_RISCV_JAL and R_RISCV_RVC_JUMP relocations.
+
+ However, consider that linker may relax the R_RISCV_CALL
+ relocations to R_RISCV_JAL or R_RISCV_RVC_JUMP, if
+ these relocations are relocated to the plt entries,
+ then we won't report error for them.
+
+ Perhaps we also need the similar checks for the
+ R_RISCV_BRANCH and R_RISCV_RVC_BRANCH relocations. */
+ msg = bfd_asprintf (_("%%X%%P: relocation %s against `%s'"
+ " which may bind externally"
+ " can not be used"
+ " when making a shared object;"
+ " recompile with -fPIC\n"),
+ howto->name, h->root.root.string);
+ r = bfd_reloc_notsupported;
}
break;
@@ -5365,9 +5369,9 @@ _bfd_riscv_relax_section (bfd *abfd, asection *sec,
undefined_weak = true;
}
- /* This line has to match the check in riscv_elf_relocate_section
- in the R_RISCV_CALL[_PLT] case. */
- if (bfd_link_pic (info) && h->plt.offset != MINUS_ONE)
+ /* This line has to match the via_pltcheck in
+ riscv_elf_relocate_section in the R_RISCV_CALL[_PLT] case. */
+ if (h->plt.offset != MINUS_ONE)
{
sym_sec = htab->elf.splt;
symval = h->plt.offset;
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