[PATCH 6/9] perf symbols: Allow for .plt without header

Adrian Hunter
2023-01-27T17:03:57Z

A static executable can have a .plt due to the presence of IFUNCs.
In that case the .plt does not have a header. Check for whether
there is a header by comparing the number of entries to the
number of relocation entries.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
tools/perf/util/symbol-elf.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index a002fc0bea03..8f7802097c72 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -489,6 +489,7 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)
Elf *elf;
int nr = 0, err = -1;
struct rel_info ri = { .is_rela = false };
+ bool lazy_plt;

elf = ss->elf;
ehdr = ss->ehdr;
@@ -523,8 +524,10 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)
plt_sym->end = plt_sym->start + shdr_plt.sh_size;
/* Use .plt.sec offset */
plt_offset = plt_sec_shdr.sh_offset;
+ lazy_plt = false;
} else {
- plt_offset = shdr_plt.sh_offset + plt_header_size;
+ plt_offset = shdr_plt.sh_offset;
+ lazy_plt = true;
}

scn_dynsym = ss->dynsym;
@@ -577,6 +580,17 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)

ri.is_rela = shdr_rel_plt.sh_type == SHT_RELA;

+ if (lazy_plt) {
+ /*
+ * Assume a .plt with the same number of entries as the number
+ * of relocation entries is not lazy and does not have a header.
+ */
+ if (ri.nr_entries * plt_entry_size == shdr_plt.sh_size)
+ dso__delete_symbol(dso, plt_sym);
+ else
+ plt_offset += plt_header_size;
+ }
+
/*
* x86 doesn't insert IFUNC relocations in .plt order, so sort to get
* back in order.
--
2.34.1