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[PATCH v1] GAS: Keep symbols in their own section [PR27566]

Xiao Zeng zengxiao@eswincomputing.com
Wed Oct 23 07:04:27 GMT 2024 
2024-10-23 14:45  Xiao Zeng <zengxiao@eswincomputing.com> wrote:
>
>2024-10-23 12:43  Alan Modra <amodra@gmail.com> wrote:
>>
>>On Tue, Oct 22, 2024 at 05:43:18PM +0800, Xiao Zeng wrote:
>>> PR27566 is categorized under ld:
>>> <https://sourceware.org/bugzilla/show_bug.cgi?id=27566>
>>> but the root cause of this issue is in gas.
>>>
>>> The following assembly example is provided:
>>>         .section        .rodata
>>>         .globl Sym
>>>         .type  Sym, @object
>>>         .set   Sym, . + 0x1200
>>>         .size	Sym, 8
>>>
>>> readelf reads ELF information:
>>> Section Headers:
>>>   [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
>>>   [ 4] .rodata           PROGBITS        0000000000000000 000040 000000 00   A  0   0  1
>>>
>>> Symbol table '.symtab' contains 7 entries:
>>>    Num:    Value          Size Type    Bind   Vis      Ndx Name
>>>      6: 0000000000001200     8 OBJECT  GLOBAL DEFAULT    4 Sym
>>>
>>> The Sym belongs to the .rodata section, but the size of .rodata is 0.
>>
>>It is not unreasonable to define a symbol relative to some section
>>with a value outside of the section.  Automatically extending a
>>section to enclose a symbol should only happen in special cases.
>>Patch rejected.
>>
>>--
>>Alan Modra
>
>Dear maintainer, thank you for your reply. I think I should provide more detailed information:
>The test case <abs-run.c> is in:
><https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/testsuite/gcc.target/riscv/rvv/autovec/unop/abs-run.c;h=f3be58ec4938e1ae8b125da3e6796f8e448b04df;hb=ee030b28004eade3da872e7ae62a526a2940a705>
>
>1 Compilation command：
>riscv64-unknown-elf-gcc                                                                                     \
>-fno-schedule-insns -mcmodel=medlow -march=rv64gcv_zvfh -mabi=lp64d \
>-O3 -mrvv-max-lmul=m4 -mrvv-vector-bits=zvl -ffast-math                            \
>-fdata-sections abs-run.c -S -o abs-run.c.upstream.s
> 

The key assembly information is:
	.section	.rodata
	.align	3
	.set	.LANCHOR0,. + 0
	.set	.LANCHOR1,. + 4096

>Compiler version information:
>Supported LTO compression algorithms: zlib
>gcc version 15.0.0 20240912 (experimental) (g3f212eabbba-dirty)
>
>2 Assembly command：
>riscv64-unknown-elf-as abs-run.c.upstream.s -o abs-run.c.upstream.s.o
>
>3 readelf outputs the information：
>riscv64-unknown-elf-readelf -SsW abs-run.c.upstream.o > abs-run.c.upstream.o.txt
>
>Section Headers:
>  [Nr] Name              Type                   Address                      Off    Size   ES Flg Lk Inf Al
>  [ 9] .rodata           PROGBITS        0000000000000000 000c78 000d80 00   A  0   0  8
>
>Symbol table '.symtab' contains 110 entries:
>   Num:    Value          Size Type    Bind   Vis      Ndx Name
>     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND 
>     1: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS abs-run.c
>    12: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT    9 .LANCHOR0
>    13: 0000000000001000     0 NOTYPE  LOCAL  DEFAULT    9 .LANCHOR1
>
>This situation, where a symbol is in a section but the section's size is insufficient to contain the symbol, does exist.
>
>Thanks
>Xiao Zeng
>
Thanks
Xiao Zeng
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