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6l: use ELF32 (ELFCLASS32) format for Plan9 ELF output #147

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

6l: use ELF32 (ELFCLASS32) format for Plan9 ELF output #147

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11 changes: 8 additions & 3 deletions sys/src/cmd/6l/asm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -190,7 +190,7 @@ asmbelf(long textfoff, vlong datafoff, vlong datva)
eh->ident[EI_MAG1] = ELFMAG1;
eh->ident[EI_MAG2] = ELFMAG2;
eh->ident[EI_MAG3] = ELFMAG3;
eh->ident[EI_CLASS] = ELFCLASS64;
eh->ident[EI_CLASS] = ELFCLASS32; /* Plan9 kernel exec requires ELF32 */
eh->ident[EI_DATA] = ELFDATA2LSB;
eh->ident[EI_VERSION] = EV_CURRENT;
eh->type = ET_EXEC;
Expand All @@ -207,7 +207,11 @@ asmbelf(long textfoff, vlong datafoff, vlong datva)
}

/*
* asmb_elf: assemble ELF64 output (called by asmb when HEADTYPE==5).
* asmb_elf: assemble ELF32/AMD64 output (called by asmb when HEADTYPE==5).
*
* Plan9's kernel exec only accepts ELF32 format (ELFCLASS32), even on amd64.
* This matches the original 6l -H5 behaviour (cput(1) = ELFCLASS32 in case 5).
* All Plan9 userspace addresses fit in 32 bits, so ELF32 is sufficient.
*/
static void
asmb_elf(void)
Expand All @@ -218,8 +222,9 @@ asmb_elf(void)
uchar *op1;
vlong datva, datafoff, pad;

/* Initialize ELF state */
/* Initialize ELF state, then force ELF32 for Plan9 compatibility */
elfinit();
elfforce32();

/* NULL section header must be at index 0 — before any other shdr */
newElfShdr(0);
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13 changes: 13 additions & 0 deletions sys/src/cmd/ld/elf.c
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Expand Up @@ -69,6 +69,19 @@ elfinit(void)
}
}

/* elfforce32: switch to ELF32 format after elfinit().
* Plan9's kernel exec only accepts ELF32, even on amd64. */
Comment on lines +72 to +73

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

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medium

The comment style for elfforce32 is inconsistent with the standard Plan 9 multi-line comment style used elsewhere in the project. It is recommended to use the standard format for better maintainability and consistency.

/*
 * elfforce32: switch to ELF32 format after elfinit().
 * Plan9's kernel exec only accepts ELF32, even on amd64.
 */

void
elfforce32(void)
{
elf64 = 0;
hdr.phoff = ELF32HDRSIZE;
hdr.shoff = ELF32HDRSIZE;
hdr.ehsize = ELF32HDRSIZE;
hdr.phentsize = ELF32PHDRSIZE;
hdr.shentsize = ELF32SHDRSIZE;
Comment on lines +77 to +82

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

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medium

The elfforce32 function should also update hdr.ident[EI_CLASS] to ELFCLASS32 to ensure the global hdr structure remains internally consistent after the format switch. While asmbelf currently overwrites this field, keeping elfforce32 self-contained prevents potential issues if hdr is used elsewhere before being fully re-initialized.

	elf64 = 0;
	hdr.ident[EI_CLASS] = ELFCLASS32;
	hdr.phoff = ELF32HDRSIZE;
	hdr.shoff = ELF32HDRSIZE;
	hdr.ehsize = ELF32HDRSIZE;
	hdr.phentsize = ELF32PHDRSIZE;
	hdr.shentsize = ELF32SHDRSIZE;

}

ElfEhdr*
getElfEhdr(void)
{
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1 change: 1 addition & 0 deletions sys/src/cmd/ld/elf.h
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Expand Up @@ -209,6 +209,7 @@ struct Elf_Note

/* Declarations */
void elfinit(void);
void elfforce32(void);
ElfEhdr* getElfEhdr(void);
ElfShdr* newElfShdr(vlong);
ElfPhdr* newElfPhdr(void);
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