* [musl] [PATCH] ldso: support DT_RELR relative relocation format
@ 2022-06-06 6:16 Fangrui Song
2022-06-23 2:12 ` [musl] " Fangrui Song
2022-08-02 19:16 ` [musl] " Rich Felker
0 siblings, 2 replies; 5+ messages in thread
From: Fangrui Song @ 2022-06-06 6:16 UTC (permalink / raw)
To: musl; +Cc: Fangrui Song
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
^ permalink raw reply [flat|nested] 5+ messages in thread
* [musl] Re: [PATCH] ldso: support DT_RELR relative relocation format
2022-06-06 6:16 [musl] [PATCH] ldso: support DT_RELR relative relocation format Fangrui Song
@ 2022-06-23 2:12 ` Fangrui Song
2022-07-16 8:23 ` Fangrui Song
2022-08-02 19:16 ` [musl] " Rich Felker
1 sibling, 1 reply; 5+ messages in thread
From: Fangrui Song @ 2022-06-23 2:12 UTC (permalink / raw)
To: musl
On 2022-06-05, Fangrui Song wrote:
>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.
Ping
^ permalink raw reply [flat|nested] 5+ messages in thread
* [musl] Re: [PATCH] ldso: support DT_RELR relative relocation format
2022-06-23 2:12 ` [musl] " Fangrui Song
@ 2022-07-16 8:23 ` Fangrui Song
0 siblings, 0 replies; 5+ messages in thread
From: Fangrui Song @ 2022-07-16 8:23 UTC (permalink / raw)
To: musl
On Wed, Jun 22, 2022 at 7:12 PM Fangrui Song <i@maskray.me> wrote:
>
> On 2022-06-05, Fangrui Song wrote:
> >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.
>
> Ping
Ping^2
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [musl] [PATCH] ldso: support DT_RELR relative relocation format
2022-06-06 6:16 [musl] [PATCH] ldso: support DT_RELR relative relocation format Fangrui Song
2022-06-23 2:12 ` [musl] " Fangrui Song
@ 2022-08-02 19:16 ` Rich Felker
2022-08-02 20:17 ` Fangrui Song
1 sibling, 1 reply; 5+ messages in thread
From: Rich Felker @ 2022-08-02 19:16 UTC (permalink / raw)
To: Fangrui Song; +Cc: musl
On Sun, Jun 05, 2022 at 11:16:33PM -0700, Fangrui Song wrote:
> 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;
> + }
> +}
> +
As written, this code is assuming !FDPIC, so should probably be
conditional on that. However I think it can be written not to make
this assumption, as:
*reloc_addr = laddr(dso, *reloc_addr);
reloc_addr++;
instead of:
*reloc_addr++ += base;
and likewise in the second instance. The laddr() macro exists
specifically to abstract translating "addresss in space of ELF image"
to "address as mapped in memory" which I think is the intended
semantic here. Is that correct?
> 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
I was concerned about the decode_vec [0] slot bitmask usage, but you
addressed that, and I've checked for other instances that might be
wrong but couldn't find any, so I think it's okay.
Rich
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [musl] [PATCH] ldso: support DT_RELR relative relocation format
2022-08-02 19:16 ` [musl] " Rich Felker
@ 2022-08-02 20:17 ` Fangrui Song
0 siblings, 0 replies; 5+ messages in thread
From: Fangrui Song @ 2022-08-02 20:17 UTC (permalink / raw)
To: musl
On 2022-08-02, Rich Felker wrote:
>On Sun, Jun 05, 2022 at 11:16:33PM -0700, Fangrui Song wrote:
>> 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;
>> + }
>> +}
>> +
>
>As written, this code is assuming !FDPIC, so should probably be
>conditional on that. However I think it can be written not to make
>this assumption, as:
>
> *reloc_addr = laddr(dso, *reloc_addr);
> reloc_addr++;
>
>instead of:
>
> *reloc_addr++ += base;
>
>and likewise in the second instance. The laddr() macro exists
>specifically to abstract translating "addresss in space of ELF image"
>to "address as mapped in memory" which I think is the intended
>semantic here. Is that correct?
I have to confess I don't know much about FDPIC (I merely read a little
bit about "ARM FDPIC ABI" a while ago.)
DT_RELR operations should resemble REL_RELATIVE for REL/RELA.
The REL_RELATIVE code does
*reloc_addr = (size_t)base + addend;
so I think `*reloc_addr++ += (size_t)base;` is fine.
>> 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
>
>I was concerned about the decode_vec [0] slot bitmask usage, but you
>addressed that, and I've checked for other instances that might be
>wrong but couldn't find any, so I think it's okay.
>
>Rich
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2022-08-02 20:18 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-06-06 6:16 [musl] [PATCH] ldso: support DT_RELR relative relocation format Fangrui Song
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
Code repositories for project(s) associated with this public inbox
https://git.vuxu.org/mirror/musl/
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).