Re: [PATCH][WIP] libiberty: Support for relocation output

[Rishi Raj <rishiraj45035@gmail.com>]

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On Mon, 23 Oct 2023 at 16:30, Jan Hubicka <hubicka@ucw.cz> wrote:

> > This patch teaches libiberty to output X86-64 Relocations.
> Hello,
> for actual patch submission you will need to add changelog :)
>
I know, right :).

> > diff --git a/libiberty/simple-object-elf.c
> b/libiberty/simple-object-elf.c
> > index 86b7a27dc74..0bbaf4b489f 100644
> > --- a/libiberty/simple-object-elf.c
> > +++ b/libiberty/simple-object-elf.c
> > @@ -238,6 +238,7 @@ typedef struct
> >  #define STT_NOTYPE 0 /* Symbol type is unspecified */
> >  #define STT_OBJECT 1 /* Symbol is a data object */
> >  #define STT_FUNC 2 /* Symbol is a code object */
> > +#define STT_SECTION 3 /* Symbol is associate with a section */
> Associated I guess.
> >  #define STT_TLS 6 /* Thread local data object */
> >  #define STT_GNU_IFUNC 10 /* Symbol is an indirect code object */
> >
> > @@ -248,6 +249,63 @@ typedef struct
> >  #define STV_DEFAULT 0 /* Visibility is specified by binding type */
> >  #define STV_HIDDEN 2 /* Can only be seen inside currect component */
> >
> > +typedef struct
> > +{
> > +  unsigned char r_offset[4]; /* Address */
> > +  unsigned char r_info[4];  /* relocation type and symbol index */
> > +} Elf32_External_Rel;
> > +
> > +typedef struct
> > +{
> > +  unsigned char r_offset[8]; /* Address */
> > +  unsigned char r_info[8]; /* Relocation type and symbol index */
> > +} Elf64_External_Rel;
> > +typedef struct
> > +{
> > +  unsigned char r_offset[4]; /* Address */
> > +  unsigned char r_info[4];  /* Relocation type and symbol index */
> > +  char r_addend[4]; /* Addend */
> > +} Elf32_External_Rela;
> > +typedef struct
> > +{
> > +  unsigned char r_offset[8]; /* Address */
> > +  unsigned char r_info[8]; /* Relocation type and symbol index */
> > +  unsigned char r_addend[8]; /* Addend */
> > +} Elf64_External_Rela;
> > +
> > +/* How to extract and insert information held in the r_info field.  */
> > +
> > +#define ELF32_R_SYM(val) ((val) >> 8)
> > +#define ELF32_R_TYPE(val) ((val) & 0xff)
> > +#define ELF32_R_INFO(sym, type) (((sym) << 8) + ((type) & 0xff))
> > +
> > +#define ELF64_R_SYM(i) ((i) >> 32)
> > +#define ELF64_R_TYPE(i) ((i) & 0xffffffff)
> > +#define ELF64_R_INFO(sym,type) ((((unsigned long) (sym)) << 32) +
> (type))
> > +
> > +/* AMD x86-64 relocations.  */
> > +#define R_X86_64_NONE 0 /* No reloc */
> > +#define R_X86_64_64 1 /* Direct 64 bit  */
> > +#define R_X86_64_PC32 2 /* PC relative 32 bit signed */
> > +#define R_X86_64_GOT32 3 /* 32 bit GOT entry */
> > +#define R_X86_64_PLT32 4 /* 32 bit PLT address */
> > +#define R_X86_64_COPY 5 /* Copy symbol at runtime */
> > +#define R_X86_64_GLOB_DAT 6 /* Create GOT entry */
> > +#define R_X86_64_JUMP_SLOT 7 /* Create PLT entry */
> > +#define R_X86_64_RELATIVE 8 /* Adjust by program base */
> > +#define R_X86_64_GOTPCREL 9 /* 32 bit signed PC relative
> > +   offset to GOT */
> > +#define R_X86_64_32 10 /* Direct 32 bit zero extended */
> > +#define R_X86_64_32S 11 /* Direct 32 bit sign extended */
> > +#define R_X86_64_16 12 /* Direct 16 bit zero extended */
>
> This will eventually need to go into per-architecture table.
> You support only those needed for Dwarf2out ouptut, right?
>
Yeah, as of now.

>
> I think we need Iant's opinion on thi part of patch (he is the
> maintainer of simple-object) but to me it looks reasonable. For longer
> term it will be necessary to think how to make this extensible to other
> architectures without writting too much of code.  (have some more
> declarative way to specify relocations we output)
>
Make sense.

>
> Honza
>