@samitouri / QOSamiQemu / commits / 156e536a7b

linux-user: Fix AT_PHDR when program headers are relocated into their own segment

When a binary is patched or relocated such that the program header table is moved into a separate PT_LOAD segment (rather than sitting at the start of the first loadable segment), QEMU's AT_PHDR auxv entry becomes incorrect. The loader was computing AT_PHDR as load_addr + e_phoff, which assumes the headers are mapped 1:1 from file offset 0. This breaks when the headers are elsewhere. The Linux kernel instead locates the PT_LOAD segment that contains e_phoff, then computes the in-memory address as p_vaddr + (e_phoff - p_offset). This correctly handles relocated headers. Fix by: 1. Add phdr_addr field to image_info to cache the resolved address. 2. Initialize to load_addr + e_phoff (fallback for headers outside any PT_LOAD). 3. In the PT_LOAD mapping loop, detect if the segment contains e_phoff and override with the segment-relative address. 4. Use info->phdr_addr for AT_PHDR instead of the incorrect formula. Signed-off-by: Akshit Yadav <valium7171@gmail.com> Reviewed-by: Helge Deller <deller@gmx.de>

Akshit Yadav committed Jun 13, 2026 at 20:51 UTC 156e536a7b9700018aaa2437072c14e3376340a7

2 files changed +21 -1

linux-user/elfload.c

+20 -1

@@ -699,7 +699,7 @@ static abi_ulong create_elf_tables(abi_ulong p, int argc, int envc,

699 /* There must be exactly DLINFO_ITEMS entries here, or the assert

700 * on info->auxv_len will trigger.

701 */

702 - NEW_AUX_ENT(AT_PHDR, (abi_ulong)(info->load_addr + exec->e_phoff));

702 + NEW_AUX_ENT(AT_PHDR, (abi_ulong)(info->phdr_addr));

703 NEW_AUX_ENT(AT_PHENT, (abi_ulong)(sizeof (struct elf_phdr)));

704 NEW_AUX_ENT(AT_PHNUM, (abi_ulong)(exec->e_phnum));

705 NEW_AUX_ENT(AT_PAGESZ, (abi_ulong)(TARGET_PAGE_SIZE));

@@ -1469,6 +1469,12 @@ static void load_elf_image(const char *image_name, const ImageSource *src,

1469 info->data_offset = load_bias;

1470 info->load_addr = load_addr;

1471 info->entry = ehdr->e_entry + load_bias;

1472 + /*

1473 + * Fallback for AT_PHDR if the program headers do not fall within

1474 + * any PT_LOAD segment (see the loop below, which overrides this with

1475 + * the correct in-memory address when a containing segment is found).

1476 + */

1477 + info->phdr_addr = load_addr + ehdr->e_phoff;

1478 info->start_code = -1;

1479 info->end_code = 0;

1480 info->start_data = -1;

@@ -1523,6 +1529,19 @@ static void load_elf_image(const char *image_name, const ImageSource *src,

1529 vaddr_ef = vaddr + eppnt->p_filesz;

1530 vaddr_em = vaddr + eppnt->p_memsz;

1531

1532 + /*

1533 + * If this segment contains the program headers, record their

1534 + * in-memory address for AT_PHDR. This matches the kernel, which

1535 + * locates the headers via the containing PT_LOAD rather than

1536 + * assuming load_addr + e_phoff (false when the phdrs are not

1537 + * mapped 1:1 from file offset 0, e.g. relocated into their own

1538 + * segment by a binary patcher).

1539 + */

1540 + if (eppnt->p_offset <= ehdr->e_phoff &&

1541 + ehdr->e_phoff < eppnt->p_offset + eppnt->p_filesz) {

1542 + info->phdr_addr = vaddr + (ehdr->e_phoff - eppnt->p_offset);

1543 + }

1544 +

1545 /*

1546 * Some segments may be completely empty, with a non-zero p_memsz

1547 * but no backing file segment.

linux-user/qemu.h

@@ -26,6 +26,7 @@

26 struct image_info {

27 abi_ulong load_bias;

28 abi_ulong load_addr;

29 + abi_ulong phdr_addr;

30 abi_ulong start_code;

31 abi_ulong end_code;

32 abi_ulong start_data;