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libbpf: Treat .data.rel.ro as read-only data

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PIC code keeps constants with pointers, e.g. vtables, in .data.rel.ro
instead of .rodata. Nothing writes there after relocation.
libbpf treats every .data* section as writable, while the kernel looks
for pointers to functions in frozen read-only maps only.

Make .data.rel.ro and .data.rel.ro.* maps read-only and frozen like
.rodata and collect pointers to functions there.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://patch.msgid.link/20260924031042.1690890-14-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov authored and Andrii Nakryiko committed 2026-10-02 05:41:50 -07:00
1 parent 76eeb9ca9c
commit 157d83120d
1 file changed
+14
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src/libbpf.c
+14
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@@ -546,6 +546,7 @@ struct bpf_struct_ops {
#define PERCPU_SEC ".percpu"
#define BSS_SEC ".bss"
#define RODATA_SEC ".rodata"
#define DATA_REL_RO_SEC ".data.rel.ro"
#define KCONFIG_SEC ".kconfig"
#define KSYMS_SEC ".ksyms"
#define STRUCT_OPS_SEC ".struct_ops"
@@ -4062,6 +4063,17 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
err = bpf_object__add_programs(obj, data, name, idx);
if (err)
return err;
} else if (strcmp(name, DATA_REL_RO_SEC) == 0 ||
str_has_pfx(name, DATA_REL_RO_SEC ".")) {
/*
* Constants with pointers in them, e.g. vtables,
* that position independent code keeps here to
* have them relocated. There is nothing that
* writes to it after that.
*/
sec_desc->sec_type = SEC_RODATA;
sec_desc->shdr = sh;
sec_desc->data = data;
} else if (strcmp(name, DATA_SEC) == 0 ||
str_has_pfx(name, DATA_SEC ".")) {
sec_desc->sec_type = SEC_DATA;
@@ -4114,6 +4126,8 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
if (!section_have_execinstr(obj, targ_sec_idx) &&
strcmp(name, ".rel" RODATA_SEC) &&
!str_has_pfx(name, ".rel" RODATA_SEC ".") &&
strcmp(name, ".rel" DATA_REL_RO_SEC) &&
!str_has_pfx(name, ".rel" DATA_REL_RO_SEC ".") &&
strcmp(name, ".rel" STRUCT_OPS_SEC) &&
strcmp(name, ".rel" STRUCT_OPS_LINK_SEC) &&
strcmp(name, ".rel?" STRUCT_OPS_SEC) &&