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Update vesa.c

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Try to fix the vesa assembly out of the clobber 

Seems like this works now.
This commit is contained in:
Gregory Kenneth Bowne
2026-01-28 16:42:52 -08:00
committed by GitHub
parent 6590a84b72
commit 44e105d413
1 changed files with 25 additions and 17 deletions
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42
kernel/vesa.c
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@@ -61,25 +61,33 @@ bool vesa_get_mode_info(uint16_t mode, vbe_mode_info_t* info) {
return ax_ret == 0x004F;
}
// Get the VESA controller information
bool vesa_get_controller_info(vbe_controller_info_t* info) {
uint16_t eax = VBE_FUNCTION_GET_CONTROLLER_INFO;
uint32_t ebx = 0;
uint32_t ecx = 0;
uint32_t edx = 0;
uint16_t ax_ret;
// We must use Segment:Offset for BIOS
uint32_t ptr = (uint32_t)info;
uint16_t segment = (uint16_t)((ptr >> 4) & 0xF000); // Base segment
uint16_t offset = (uint16_t)(ptr & 0xFFFF); // Offset
if (vesa_bios_call(VBE_FUNCTION_GET_CONTROLLER_INFO, &eax, &ebx, &ecx, &edx)) {
// Copy controller information into the provided struct
uint32_t base = (uint32_t)info;
__asm__ __volatile__(
"movw %%bx, %%es:%%di\n"
:
: "b" (base)
: "%es", "%di", "memory"
);
return true;
}
return false;
// Copy "VBE2" into signature to tell BIOS we want VBE 2.0+ info
info->Signature[0] = 'V';
info->Signature[1] = 'B';
info->Signature[2] = 'E';
info->Signature[3] = '2';
// To fix the error: Do not use %es in clobber.
// Use a temporary register or a push/pop sequence if we MUST touch ES.
__asm__ __volatile__(
"push %%es\n\t"
"movw %1, %%es\n\t"
"int $0x10\n\t"
"pop %%es\n\t"
: "=a"(ax_ret)
: "r"(segment), "D"(offset), "a"(0x4F00)
: "memory", "cc"
);
return ax_ret == 0x004F;
}
// Return pointer to the VESA framebuffer