[PATCH] D77424: [XCOFF][AIX] Relocation support for SymB

[Digger via Phabricator via llvm-commits]

DiggerLin added inline comments.


================
Comment at: llvm/lib/MC/XCOFFObjectWriter.cpp:462
+  // SymB must be R_NEG here, given the general form of Target(MCValue) is
+  // "SymbolA - SymbolB + imm64".
+  const uint8_t TypeB = XCOFF::RelocationType::R_NEG;
----------------
DiggerLin wrote:
> I have question on the "SymbolA - SymbolB + imm64"
> 
> for example: in the assembly of the test case 
> ```
>        .csect .text[PR] 
> .foo:
> # %bb.0:                                # %entry
>         li 4, 0
>         cmplwi  3, 3
>         stw 3, -8(1)
>         stw 4, -12(1)
>         bgt     0, LBB0_5
> # %bb.1:                                # %entry
>         lwz 4, LC0(2)
>         slwi 3, 3, 2
>         lwzx 3, 3, 4
>         add 3, 3, 4
>         mtctr 3
>         bctr
> LBB0_2:                                 # %sw.bb1
>         li 3, 1
>         b LBB0_6
> 
> .......
> ........
>         .csect .rodata[RO]
>         .align  2
> .LJTI0_0: (symb)
>         .long   LBB0_2-.LJTI0_0   
> 
> ```
> the address of LBB0_2 is 44 (0x2C) .
> 
> 
> the value in the 
> 00000058 <.rodata>:
>   58:   ff ff ff d4     .long 0xffffffd4   (-0x2C)
>                 58: R_POS       .text
>                 58: R_NEG       .rodata-0x58
> 
> the jump address 
> .text+imm64 (-0x2C) - (0x58) =0x84 + LC0(R2). it not correct
> 
> I think the content of in the address of the first bytes .csect .rodata[RO] after link in  should be 
> .text - imm64(-0X2C)-(0X58) = -0X2C  + LC0(R2) ?
> 
> 
please ignore above question. I got it . the value in the address 0x58  is .text+imm64-.rodata.  
So imm64 = value in the address 0x58 + .rodata -.text
when relocation.



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  https://reviews.llvm.org/D77424/new/

https://reviews.llvm.org/D77424