From: Fangrui Song <i@maskray.me>
To: musl@lists.openwall.com
Cc: Fangrui Song <i@maskray.me>
Subject: [musl] [PATCH] ldso: support DT_RELR relative relocation format
Date: Sun, 5 Jun 2022 23:16:33 -0700 [thread overview]
Message-ID: <20220606061633.539208-1-i@maskray.me> (raw)
this resolves DT_RELR relocations in non-ldso objects.
generic-abi pre-standard for DT_RELR:
https://groups.google.com/g/generic-abi/c/bX460iggiKg
FreeBSD rtld added DT_RELR support in 2021-08.
glibc added DT_RELR support in 2022-04.
Since ld.lld 7, --pack-dyn-relocs=relr can generate DT_RELR.
Since binutils 2.38, GNU ld's x86 and powerpc64 ports supports -z
pack-relative-relocs to generate DT_RELR. ld.lld 15 also has the option.
---
Changes from https://www.openwall.com/lists/musl/2019/03/06/3
* rename some variables
* decode_vec: add `if (v[0] < 8*sizeof(long))`
---
include/elf.h | 8 ++++++--
ldso/dynlink.c | 20 +++++++++++++++++++-
src/internal/dynlink.h | 2 +-
3 files changed, 26 insertions(+), 4 deletions(-)
diff --git a/include/elf.h b/include/elf.h
index 86e2f0bb..9e980a29 100644
--- a/include/elf.h
+++ b/include/elf.h
@@ -385,7 +385,8 @@ typedef struct {
#define SHT_PREINIT_ARRAY 16
#define SHT_GROUP 17
#define SHT_SYMTAB_SHNDX 18
-#define SHT_NUM 19
+#define SHT_RELR 19
+#define SHT_NUM 20
#define SHT_LOOS 0x60000000
#define SHT_GNU_ATTRIBUTES 0x6ffffff5
#define SHT_GNU_HASH 0x6ffffff6
@@ -754,7 +755,10 @@ typedef struct {
#define DT_PREINIT_ARRAY 32
#define DT_PREINIT_ARRAYSZ 33
#define DT_SYMTAB_SHNDX 34
-#define DT_NUM 35
+#define DT_RELRSZ 35
+#define DT_RELR 36
+#define DT_RELRENT 37
+#define DT_NUM 38
#define DT_LOOS 0x6000000d
#define DT_HIOS 0x6ffff000
#define DT_LOPROC 0x70000000
diff --git a/ldso/dynlink.c b/ldso/dynlink.c
index 5b9c8be4..a50ef00a 100644
--- a/ldso/dynlink.c
+++ b/ldso/dynlink.c
@@ -208,7 +208,8 @@ static void decode_vec(size_t *v, size_t *a, size_t cnt)
size_t i;
for (i=0; i<cnt; i++) a[i] = 0;
for (; v[0]; v+=2) if (v[0]-1<cnt-1) {
- a[0] |= 1UL<<v[0];
+ if (v[0] < 8*sizeof(long))
+ a[0] |= 1UL<<v[0];
a[v[0]] = v[1];
}
}
@@ -513,6 +514,22 @@ static void do_relocs(struct dso *dso, size_t *rel, size_t rel_size, size_t stri
}
}
+static void do_relr_relocs(struct dso *dso, size_t *relr, size_t relr_size) {
+ unsigned char *base = dso->base;
+ size_t *reloc_addr;
+ for (; relr_size; relr++, relr_size-=sizeof(size_t))
+ if ((relr[0]&1) == 0) {
+ reloc_addr = laddr(dso, relr[0]);
+ *reloc_addr++ += (size_t)base;
+ } else {
+ int i = 0;
+ for (size_t bitmap=relr[0]; (bitmap>>=1); i++)
+ if (bitmap&1)
+ reloc_addr[i] += (size_t)base;
+ reloc_addr += 8*sizeof(size_t)-1;
+ }
+}
+
static void redo_lazy_relocs()
{
struct dso *p = lazy_head, *next;
@@ -1355,6 +1372,7 @@ static void reloc_all(struct dso *p)
2+(dyn[DT_PLTREL]==DT_RELA));
do_relocs(p, laddr(p, dyn[DT_REL]), dyn[DT_RELSZ], 2);
do_relocs(p, laddr(p, dyn[DT_RELA]), dyn[DT_RELASZ], 3);
+ do_relr_relocs(p, laddr(p, dyn[DT_RELR]), dyn[DT_RELRSZ]);
if (head != &ldso && p->relro_start != p->relro_end &&
mprotect(laddr(p, p->relro_start), p->relro_end-p->relro_start, PROT_READ)
diff --git a/src/internal/dynlink.h b/src/internal/dynlink.h
index 51c0639f..830354eb 100644
--- a/src/internal/dynlink.h
+++ b/src/internal/dynlink.h
@@ -93,7 +93,7 @@ struct fdpic_dummy_loadmap {
#endif
#define AUX_CNT 32
-#define DYN_CNT 32
+#define DYN_CNT 37
typedef void (*stage2_func)(unsigned char *, size_t *);
--
2.36.1
next reply other threads:[~2022-06-06 6:16 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-06 6:16 Fangrui Song [this message]
2022-06-23 2:12 ` [musl] " Fangrui Song
2022-07-16 8:23 ` Fangrui Song
2022-08-02 19:16 ` [musl] " Rich Felker
2022-08-02 20:17 ` Fangrui Song
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