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6l: fix text PT_LOAD to use Plan9 ELF convention (off=HEADR, vaddr=IN… #146

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Merged
staalmannen merged 1 commit into from
May 22, 2026
Merged

6l: fix text PT_LOAD to use Plan9 ELF convention (off=HEADR, vaddr=IN… #146

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12 changes: 6 additions & 6 deletions sys/src/cmd/6l/asm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -109,12 +109,12 @@ asmbelf(long textfoff, vlong datafoff, vlong datva)
ph = newElfPhdr();
ph->type = PT_LOAD;
ph->flags = PF_R | PF_X;
ph->off = 0; /* cover ELF header from offset 0 */
ph->vaddr = INITTEXT - textfoff; /* 0x200C00 - 0xC00 = 0x200000 */
ph->paddr = INITTEXT - textfoff;
ph->filesz = textfoff + textsize; /* header area + text */
ph->memsz = textfoff + textsize;
ph->align = 0x1000;
ph->off = textfoff; /* HEADR=0xC00; Plan9 convention: off=HEADR not 0 */
ph->vaddr = INITTEXT; /* 0x200C00; alignment ok: 0xC00 ≡ 0x200C00 (mod 0x200000) */
ph->paddr = INITTEXT;
ph->filesz = textsize;
ph->memsz = textsize;
ph->align = INITRND; /* 0x200000 */
Comment on lines +112 to +117

@gemini-code-assist gemini-code-assist Bot May 22, 2026

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medium

The alignment constraint vaddr % align == off % align now depends on textfoff matching the sub-page offset of INITTEXT (e.g., 0xC00). While this works for the current fixed header size, it is fragile. If textfoff changes (e.g., due to additional program headers), the ELF alignment requirement will be violated for the 2MB INITRND. Consider adding a check to ensure textfoff % INITRND == INITTEXT % INITRND to prevent generating malformed binaries if the header size ever deviates.


ph = newElfPhdr();
ph->type = PT_LOAD;
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