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pc99/acpi: fix interrupt source override padding (#1665)

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By splitting the u32 into 2x u16 we lower the alignment requirements
of the compiler. So now sizeof(acpi_madt_iso_t) is equal to the true
size.

Fixes an early boot triple fault caused by UBSAN alignment checks during
MADT parsing.

Signed-off-by: Bill Nguyen <bill.nguyen@unsw.edu.au>
This commit is contained in:
Bill Nguyen 2026-06-12 14:41:09 +10:00 committed by GitHub
parent 868454e1d6
commit edcb605fee
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GPG key ID: B5690EEEBB952194
1 changed files with 10 additions and 12 deletions
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22
src/plat/pc99/machine/acpi.c
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@ -143,14 +143,13 @@ typedef struct acpi_madt_iso {
acpi_madt_header_t header;
uint8_t bus; /* always 0 (ISA) */
uint8_t source;
uint32_t gsi;
/* Split the u32 into 2x u16 to prevent the compiler from padding the struct. */
uint16_t gsi_low;
uint16_t gsi_high;
uint16_t flags;
} acpi_madt_iso_t;
/* We can't assert on the sizeof acpi_madt_iso because it contains trailing
* padding.
*/
unverified_compile_assert(acpi_madt_iso_packed,
OFFSETOF(acpi_madt_iso_t, flags) == sizeof(acpi_madt_header_t) + 6)
compile_assert(acpi_madt_iso_packed,
sizeof(acpi_madt_iso_t) == sizeof(acpi_madt_header_t) + 8)
/* workaround because string literals are not supported by C parser */
const char acpi_str_rsd[] = {'R', 'S', 'D', ' ', 'P', 'T', 'R', ' ', 0};
@ -358,13 +357,12 @@ BOOT_CODE uint32_t acpi_madt_scan(
(*num_ioapic)++;
}
break;
case MADT_ISO:
printf("ACPI: MADT_ISO bus=%d source=%d gsi=%d flags=0x%x\n",
((acpi_madt_iso_t *)acpi_madt_header)->bus,
((acpi_madt_iso_t *)acpi_madt_header)->source,
((acpi_madt_iso_t *)acpi_madt_header)->gsi,
((acpi_madt_iso_t *)acpi_madt_header)->flags);
case MADT_ISO: {
UNUSED acpi_madt_iso_t *iso = (acpi_madt_iso_t *)acpi_madt_header;
printf("ACPI: MADT_ISO bus=%d source=%d gsi=0x%x%02x flags=0x%x\n",
iso->bus, iso->source, iso->gsi_high, iso->gsi_low, iso->flags);
break;
}
default:
break;
}