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Re: [PATCH: PR gas/11323] Add R_ARM_GOT_PREL relocation to arm assembler

From: Carrot Wei <carrot at google dot com>
To: Richard Earnshaw <rearnsha at arm dot com>
Cc: binutils at sourceware dot org
Date: Mon, 15 Mar 2010 17:14:41 +0800
Subject: Re: [PATCH: PR gas/11323] Add R_ARM_GOT_PREL relocation to arm assembler
References: <7587b291003150137x3f5a3efqdbe1149c15d8ff2f@mail.gmail.com> <1268643095.16897.19.camel@e200601-lin.cambridge.arm.com>

Specify GOT_PREL and get GOT_PREL sounds more logical.  I will modify
my patch in this way.

thanks
Guozhi

On Mon, Mar 15, 2010 at 4:51 PM, Richard Earnshaw <rearnsha@arm.com> wrote:
>
> On Mon, 2010-03-15 at 16:37 +0800, Carrot Wei wrote:
>> Hi
>>
>> ? As described in http://sourceware.org/bugzilla/show_bug.cgi?id=11323, this
>> patch processes following expression
>>
>> ? ? ? .word ? var(GOTABS)-(.LPIC0+4)
>>
>> And produces a relocation of type R_ARM_GOT_PREL.
>>
>> This patch has been tested by "make check-gas".
>>
>
> I understand why you've done it this way, but I don't like the fact that
> the (GOTABS) annotation leads to a GOT_PREL relocation. ?I think the
> correct way of expressing this is to have a GOT_PREL annotation itself,
> and then to factor compensation for the addend into the remainder of the
> expression:
>
> So, mathematically
> ? ? ? ?var(GOT_PREL) = &GOT_SLOT(var) - .
>
> and the expression that should then be used in the assembly should
> compensate for this:
>
> ? ? ? ?.word var(GOT_PREL) - (.LPIC0+4 - .)
>
> The advantage of this way of expressing things is that we've now got two
> parts to the expression: a var (with relocation type) and and addend
> (that's constant). ?Further, if the addend is zero, then the expression
> collapses naturally to '.word var(GOT_PREL)' and we still get exactly
> the right output.
>
> R.
>
>> thanks
>> Wei Guozhi
>>
>> bfd/
>> 2010-03-15 ?Wei Guozhi ?<carrot@google.com>
>>
>> ? ? ? ? PR gas/11323
>> ? ? ? ? * bfd-in2.h (enum bfd_reloc_code_real): New BFD_RELOC_* types.
>> ? ? ? ? * elf32-arm.c (elf32_arm_reloc_map): New BFD_RELOC_* to R_ARM_* maps.
>> ? ? ? ? * libbfd.h (bfd_reloc_code_real_names): New BFD_RELOC_* names.
>> ? ? ? ? * reloc.c (comments): Document the new relocations.
>>
>> gas/
>> 2010-03-15 ?Wei Guozhi ?<carrot@google.com>
>>
>> ? ? ? ? PR gas/11323
>> ? ? ? ? * config/tc-arm.c (reloc_names): New relocation names.
>> ? ? ? ? (md_apply_fix): New case for BFD_RELOC_ARM_GOT_ABS.
>> ? ? ? ? (tc_gen_reloc): New case for BFD_RELOC_ARM_GOT_PREL.
>> ? ? ? ? * doc/c-arm.texi (ARM-Relocations): Document the new relocation.
>>
>> gas/testsuite
>> 2010-03-15 ?Wei Guozhi ?<carrot@google.com>
>>
>> ? ? ? ? PR gas/11323
>> ? ? ? ? * gas/arm/got_prel.s: New test case.
>> ? ? ? ? * gas/arm/got_prel.d: Likewise.
>>
>>
>> Index: bfd-in2.h
>> ===================================================================
>> RCS file: /cvs/src/src/bfd/bfd-in2.h,v
>> retrieving revision 1.507
>> diff -u -r1.507 bfd-in2.h
>> --- bfd-in2.h ? 8 Feb 2010 20:28:43 -0000 ? ? ? 1.507
>> +++ bfd-in2.h ? 15 Mar 2010 08:07:00 -0000
>> @@ -3114,6 +3114,8 @@
>> ? ?BFD_RELOC_ARM_RELATIVE,
>> ? ?BFD_RELOC_ARM_GOTOFF,
>> ? ?BFD_RELOC_ARM_GOTPC,
>> + ?BFD_RELOC_ARM_GOT_ABS,
>> + ?BFD_RELOC_ARM_GOT_PREL,
>>
>> ?/* ARM thread-local storage relocations. ?*/
>> ? ?BFD_RELOC_ARM_TLS_GD32,
>>
>>
>> Index: elf32-arm.c
>> ===================================================================
>> RCS file: /cvs/src/src/bfd/elf32-arm.c,v
>> retrieving revision 1.227
>> diff -u -r1.227 elf32-arm.c
>> --- elf32-arm.c 4 Mar 2010 17:16:08 -0000 ? ? ? 1.227
>> +++ elf32-arm.c 15 Mar 2010 08:07:02 -0000
>> @@ -1721,6 +1721,8 @@
>> ? ? ?{BFD_RELOC_ARM_RELATIVE, ? ? ? ? R_ARM_RELATIVE},
>> ? ? ?{BFD_RELOC_ARM_GOTOFF, ? ? ? ? ? R_ARM_GOTOFF32},
>> ? ? ?{BFD_RELOC_ARM_GOTPC, ? ? ? ? ? ?R_ARM_GOTPC},
>> + ? ?{BFD_RELOC_ARM_GOT_ABS, ? ? ? ? ?R_ARM_GOT_ABS},
>> + ? ?{BFD_RELOC_ARM_GOT_PREL, ? ? ? ? R_ARM_GOT_PREL},
>> ? ? ?{BFD_RELOC_ARM_GOT32, ? ? ? ? ? ?R_ARM_GOT32},
>> ? ? ?{BFD_RELOC_ARM_PLT32, ? ? ? ? ? ?R_ARM_PLT32},
>> ? ? ?{BFD_RELOC_ARM_TARGET1, ? ? ? ? R_ARM_TARGET1},
>>
>>
>> Index: libbfd.h
>> ===================================================================
>> RCS file: /cvs/src/src/bfd/libbfd.h,v
>> retrieving revision 1.227
>> diff -u -r1.227 libbfd.h
>> --- libbfd.h ? ?8 Feb 2010 20:28:43 -0000 ? ? ? 1.227
>> +++ libbfd.h ? ?15 Mar 2010 08:07:02 -0000
>> @@ -1330,6 +1330,8 @@
>> ? ?"BFD_RELOC_ARM_RELATIVE",
>> ? ?"BFD_RELOC_ARM_GOTOFF",
>> ? ?"BFD_RELOC_ARM_GOTPC",
>> + ?"BFD_RELOC_ARM_GOT_ABS",
>> + ?"BFD_RELOC_ARM_GOT_PREL",
>> ? ?"BFD_RELOC_ARM_TLS_GD32",
>> ? ?"BFD_RELOC_ARM_TLS_LDO32",
>> ? ?"BFD_RELOC_ARM_TLS_LDM32",
>>
>>
>> Index: reloc.c
>> ===================================================================
>> RCS file: /cvs/src/src/bfd/reloc.c,v
>> retrieving revision 1.198
>> diff -u -r1.198 reloc.c
>> --- reloc.c ? ? 21 Feb 2010 22:24:03 -0000 ? ? ?1.198
>> +++ reloc.c ? ? 15 Mar 2010 08:07:03 -0000
>> @@ -2940,6 +2940,10 @@
>> ? ?BFD_RELOC_ARM_GOTOFF
>> ?ENUMX
>> ? ?BFD_RELOC_ARM_GOTPC
>> +ENUMX
>> + ?BFD_RELOC_ARM_GOT_ABS
>> +ENUMX
>> + ?BFD_RELOC_ARM_GOT_PREL
>> ?ENUMDOC
>> ? ?Relocations for setting up GOTs and PLTs for shared libraries.
>>
>>
>> Index: config/tc-arm.c
>> ===================================================================
>> RCS file: /cvs/src/src/gas/config/tc-arm.c,v
>> retrieving revision 1.437
>> diff -u -r1.437 tc-arm.c
>> --- config/tc-arm.c ? ? 5 Mar 2010 10:41:04 -0000 ? ? ? 1.437
>> +++ config/tc-arm.c ? ? 15 Mar 2010 08:19:41 -0000
>> @@ -16191,7 +16191,8 @@
>> ? ?{ "tlsldm", ?BFD_RELOC_ARM_TLS_LDM32}, { "TLSLDM", ?BFD_RELOC_ARM_TLS_LDM32},
>> ? ?{ "tlsldo", ?BFD_RELOC_ARM_TLS_LDO32}, { "TLSLDO", ?BFD_RELOC_ARM_TLS_LDO32},
>> ? ?{ "gottpoff",BFD_RELOC_ARM_TLS_IE32}, ?{ "GOTTPOFF",BFD_RELOC_ARM_TLS_IE32},
>> - ?{ "tpoff", ? BFD_RELOC_ARM_TLS_LE32}, ?{ "TPOFF", ? BFD_RELOC_ARM_TLS_LE32}
>> + ?{ "tpoff", ? BFD_RELOC_ARM_TLS_LE32}, ?{ "TPOFF", ? BFD_RELOC_ARM_TLS_LE32},
>> + ?{ "gotabs", ?BFD_RELOC_ARM_GOT_ABS}, ? { "GOTABS", ?BFD_RELOC_ARM_GOT_ABS }
>> ?};
>> ?#endif
>>
>> @@ -20477,7 +20478,13 @@
>> ? ? ? ?if (fixP->fx_done || !seg->use_rela_p)
>> ? ? ? ? md_number_to_chars (buf, 0, 4);
>> ? ? ? ?break;
>> -
>> +
>> + ? ?case BFD_RELOC_ARM_GOT_ABS:
>> + ? ? ?fixP->fx_r_type = BFD_RELOC_ARM_GOT_PREL;
>> + ? ? ?if (fixP->fx_done || !seg->use_rela_p)
>> + ? ? ? ?md_number_to_chars (buf, value, 4);
>> + ? ? ?break;
>> +
>> ? ? ?case BFD_RELOC_ARM_TARGET2:
>> ? ? ? ?/* TARGET2 is not partial-inplace, so we need to write the
>> ? ? ? ? ? addend here for REL targets, because it won't be written out
>> @@ -21062,6 +21069,7 @@
>> ?#ifdef OBJ_ELF
>> ? ? ?case BFD_RELOC_ARM_GOT32:
>> ? ? ?case BFD_RELOC_ARM_GOTOFF:
>> + ? ?case BFD_RELOC_ARM_GOT_PREL:
>> ? ? ?case BFD_RELOC_ARM_PLT32:
>> ? ? ?case BFD_RELOC_ARM_TARGET1:
>> ? ? ?case BFD_RELOC_ARM_ROSEGREL32:
>>
>>
>> Index: doc/c-arm.texi
>> ===================================================================
>> RCS file: /cvs/src/src/gas/doc/c-arm.texi,v
>> retrieving revision 1.68
>> diff -u -r1.68 c-arm.texi
>> --- doc/c-arm.texi ? ? ?18 Feb 2010 10:56:27 -0000 ? ? ?1.68
>> +++ doc/c-arm.texi ? ? ?15 Mar 2010 08:19:42 -0000
>> @@ -452,7 +452,8 @@
>> ?@code{TLSGD},
>> ?@code{TLSLDM},
>> ?@code{TLSLDO},
>> -@code{GOTTPOFF}
>> +@code{GOTTPOFF},
>> +@code{GOTABS}
>> ?and
>> ?@code{TPOFF}.
>>
>> gas/arm/got_prel.s
>> ======================================================
>> ? ? ? ? .code ? 16
>> ? ? ? ? .text
>> .Ltext0:
>> ? ? ? ? .section ? ? ? ?.text.foo,"ax",%progbits
>> ? ? ? ? .align ?2
>> ? ? ? ? .global foo
>> ? ? ? ? .code ? 16
>> ? ? ? ? .thumb_func
>> ? ? ? ? .type ? foo, %function
>> foo:
>> ? ? ? ? .fnstart
>> ? ? ? ? ldr ? ? r3, .L3
>> .LPIC0:
>> ? ? ? ? add ? ? r3, pc
>> ? ? ? ? ldr ? ? r3, [r3]
>> ? ? ? ? ldr ? ? r2, [r3]
>> ? ? ? ? str ? ? r0, [r3]
>> ? ? ? ? mov ? ? r0, r2
>> ? ? ? ? bx ? ? ?lr
>> ? ? ? ? .align ?2
>> .L3:
>> ? ? ? ? .word ? i(GOTABS) - (.LPIC0+4)
>> ? ? ? ? .fnend
>>
>>
>> gas/arm/got_prel.d
>> ======================================================
>> # name: R_ARM_GOT_PREL relocation
>> # source: got_prel.s
>> # as: -march=armv5te -meabi=5
>> # readelf: -x 4 -r
>>
>> Relocation section '.rel.text.foo' at offset 0x3f0 contains 1 entries:
>> ?Offset ? ? Info ? ?Type ? ? ? ? ? ?Sym.Value ?Sym. Name
>> 00000010 ?00000c60 R_ARM_GOT_PREL ? ?00000000 ? i
>>
>> Relocation section '.rel.ARM.exidx.text.foo' at offset 0x3f8 contains 2 entries:
>> ?Offset ? ? Info ? ?Type ? ? ? ? ? ?Sym.Value ?Sym. Name
>> 00000000 ?0000042a R_ARM_PREL31 ? ? ?00000000 ? .text.foo
>> 00000000 ?00000d00 R_ARM_NONE ? ? ? ?00000000 ? __aeabi_unwind_cpp_pr0
>>
>> Hex dump of section '.text.foo':
>> ?NOTE: This section has relocations against it, but these have NOT
>> been applied to this dump.
>> ? 0x00000000 034b7b44 1b681a68 1860101c 7047c046 .K{D.h.h.`..pG.F
>> ? 0x00000010 0a000000 ? ? ? ? ? ? ? ? ? ? ? ? ? ?....
>
>

References:
- [PATCH: PR gas/11323] Add R_ARM_GOT_PREL relocation to arm assembler
  - From: Carrot Wei
- Re: [PATCH: PR gas/11323] Add R_ARM_GOT_PREL relocation to arm assembler
  - From: Richard Earnshaw

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