[PATCH] ARC: Support R_ARC_JMP_SLOT relocations during bootstrap
I ran into this issue while trying to debug a _different_ issue witin the uClinc(-ng) arc dynamic linker. I turned on debugging support within the dynamic linker, and the linker would no longer complete its bootstrap phase due to a lack of support for the R_ARC_JMP_SLOT relocation type. To reproduce this issue it should be enough to configure uClibc(-ng) for ARC with 'DODEBUG=y', then try to run anything that requires dynamic linking. The R_ARC_JMP_SLOT relocation type is used within the .plt, so I believe it makes sense for these relocations to be generated. I updated the associated comment above the boostrap patching code so that it makes more sense (to me at least) with the extra relocation support. I wonder if you would consider merging this patch? Thanks, Andrew --- This commit adds support for R_ARC_JMP_SLOT relocations during the bootstrap phase of the dynamic linker. These relocations will be generated if uClibc is configured with 'DODEBUG=y'. --- ldso/ldso/arc/dl-startup.h | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/ldso/ldso/arc/dl-startup.h b/ldso/ldso/arc/dl-startup.h index ef89b53..fadc433 100644 --- a/ldso/ldso/arc/dl-startup.h +++ b/ldso/ldso/arc/dl-startup.h @@ -64,10 +64,11 @@ __asm__( /* * Dynamic loader bootstrapping: - * Since we don't modify text at runtime, these can only be data relos - * (so safe to assume that they are word aligned). - * And also they HAVE to be RELATIVE relos only - * @RELP is the relo entry being processed + * The only relocations that should be found are either R_ARC_RELATIVE for + * data relocations (.got, etc) or R_ARC_JMP_SLOT for code relocations + * (.plt). It is safe to assume that all of these relocations are word + * aligned. + * @RELP is the reloc entry being processed * @REL is the pointer to the address we are relocating. * @SYMBOL is the symbol involved in the relocation * @LOAD is the load address. @@ -78,6 +79,8 @@ do { \ int type = ELF32_R_TYPE((RELP)->r_info); \ if (likely(type == R_ARC_RELATIVE)) \ *REL += (unsigned long) LOAD; \ + else if (type == R_ARC_JMP_SLOT) \ + *REL = SYMBOL; \ else \ _dl_exit(1); \ }while(0) -- 2.5.1
Hi Andrew, Andrew Burgess wrote,
I ran into this issue while trying to debug a _different_ issue witin the uClinc(-ng) arc dynamic linker. I turned on debugging support within the dynamic linker, and the linker would no longer complete its bootstrap phase due to a lack of support for the R_ARC_JMP_SLOT relocation type.
To reproduce this issue it should be enough to configure uClibc(-ng) for ARC with 'DODEBUG=y', then try to run anything that requires dynamic linking.
The R_ARC_JMP_SLOT relocation type is used within the .plt, so I believe it makes sense for these relocations to be generated.
I updated the associated comment above the boostrap patching code so that it makes more sense (to me at least) with the extra relocation support.
I wonder if you would consider merging this patch?
Yes, I merged it and pushed, Thanks Waldemar
On 07/28/2016 10:59 AM, Andrew Burgess wrote:
I ran into this issue while trying to debug a _different_ issue witin the uClinc(-ng) arc dynamic linker. I turned on debugging support within the dynamic linker, and the linker would no longer complete its bootstrap phase due to a lack of support for the R_ARC_JMP_SLOT relocation type.
To reproduce this issue it should be enough to configure uClibc(-ng) for ARC with 'DODEBUG=y', then try to run anything that requires dynamic linking.
The R_ARC_JMP_SLOT relocation type is used within the .plt, so I believe it makes sense for these relocations to be generated.
I updated the associated comment above the boostrap patching code so that it makes more sense (to me at least) with the extra relocation support.
I wonder if you would consider merging this patch?
Thanks, Andrew
---
This commit adds support for R_ARC_JMP_SLOT relocations during the bootstrap phase of the dynamic linker. These relocations will be generated if uClibc is configured with 'DODEBUG=y'. --- ldso/ldso/arc/dl-startup.h | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/ldso/ldso/arc/dl-startup.h b/ldso/ldso/arc/dl-startup.h index ef89b53..fadc433 100644 --- a/ldso/ldso/arc/dl-startup.h +++ b/ldso/ldso/arc/dl-startup.h @@ -64,10 +64,11 @@ __asm__(
/* * Dynamic loader bootstrapping: - * Since we don't modify text at runtime, these can only be data relos - * (so safe to assume that they are word aligned). - * And also they HAVE to be RELATIVE relos only - * @RELP is the relo entry being processed + * The only relocations that should be found are either R_ARC_RELATIVE for + * data relocations (.got, etc) or R_ARC_JMP_SLOT for code relocations + * (.plt). It is safe to assume that all of these relocations are word + * aligned. + * @RELP is the reloc entry being processed * @REL is the pointer to the address we are relocating. * @SYMBOL is the symbol involved in the relocation * @LOAD is the load address. @@ -78,6 +79,8 @@ do { \ int type = ELF32_R_TYPE((RELP)->r_info); \ if (likely(type == R_ARC_RELATIVE)) \ *REL += (unsigned long) LOAD; \ + else if (type == R_ARC_JMP_SLOT) \ + *REL = SYMBOL; \ else \ _dl_exit(1); \ }while(0)
So I know this has been merged and all - but I'm wondering if this is PIE safe. Cuper has been painfully fixing PIE related issues - including uClibc issues and since we are on the topic I'm wondering if this needs some additional fixup ? -Vineet
participants (3)
-
Andrew Burgess -
Vineet Gupta -
Waldemar Brodkorb