[metal] Show "screen of death" on VGA console upon program crash #650
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added 5 commits
October 5, 2022 16:25
If using a pre-existing VGA text console, the VGA initialization code now retrieves the cursor position & character height from the BIOS data area while still in real mode — rather than reading from the BIOS data area only after entering long mode. (This should help make the code more correct, if Cosmopolitan were to support UEFI graphics output in the future. If the program were booted via UEFI, then the long mode IsMetal() code would still be activated, but the BIOS data area might not have been initialized in that case.) This change also means that there are now a few more fields in the `struct mman`.
There is now a new function _klog_vga(), which can be called by kprintf() to output system messages — e.g. information about CPU exceptions — on the VGA screen.
jart
approved these changes
Oct 6, 2022
| @@ -188,6 +189,7 @@ privileged static void klog(const char *b, size_t n) { | |||
| : /* no inputs */ | |||
| : "a"(b[i]), "dN"(dx)); | |||
| } | |||
| if (_weaken(_klog_vga)) _weaken(_klog_vga)(b, n); | |||
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With commit 5aaadf1, the VGA console code can now display information about program crashes:
My aim in implementing a "screen of death" is to make it easier to debug program crashes on actual bare metal setups (where we will not be able to use e.g. QEMU's or Bochs's debugging features). So yes, I have tested the "screen of death" on a real machine. And it does work. 🙂
I also included a few other less major changes within this PR, namely https://github.com/tkchia/cosmopolitan/commit/9926ed74f11222d4bf0c71a1944c2e717a9552b8, https://github.com/tkchia/cosmopolitan/commit/7059a7109d3a7647ecafc3f7b178b1dd12ec83d8, and https://github.com/tkchia/cosmopolitan/commit/b8cd8a07b48b726fde2c544ea42f715e80d23a04.