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Detect and panic when running buggy qemu releases.

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Jonas 'Sortie' Termansen 2013-06-21 23:19:54 +02:00
parent 308b3169ca
commit 96e4c00c5f
1 changed files with 28 additions and 0 deletions
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28
sortix/kernel.cpp
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@ -145,6 +145,34 @@ extern "C" void KernelInit(unsigned long magic, multiboot_info_t* bootinfo)
// Display the boot welcome screen.
DoWelcome();
#if defined(__x86_64__)
// TODO: Remove this hack when qemu 1.4.x and 1.5.0 are obsolete.
// Verify that we are not running under a buggy qemu where the instruction
// movl (%eax), %esi is misinterpreted (amongst others). In this case it
// will try to access the memory at [bx + si]. We'll make sure that eax
// points to a variable on the stack that has another value than at bx + si,
// and if the values compare equal using the buggy instruction, we panic.
uint32_t intended_variable; // rax will point to here.
uint32_t is_buggy_qemu;
asm ("movq $0x1000, %%rbx\n" /* access 32-bit value at 0x1000 */
"movl (%%rbx), %%esi\n"
"subl $1, %%esi\n" /* change the 32-bit value */
"movl %%esi, (%%rax)\n" /* store the new value in intended_variable */
"movq $0x0, %%rsi\n" /* make rsi zero, so bx + si points to 0x1000 */
"movl (%%eax), %%esi\n" /* do the perhaps-buggy memory access */
"movl (%%rax), %%ebx\n" /* do a working memory access */
"movl %%ebx, %0\n" /* load the desired value into is_buggy_qemu */
"subl %%esi, %0\n" /* subtract the possibly incorrect value. */
: "=r"(is_buggy_qemu)
: "a"(&intended_variable)
: "rsi", "rbx");
if ( is_buggy_qemu )
Panic("You are running a buggy version of qemu. The 1.4.x and 1.5.0 "
"releases are known to execute some instructions incorrectly on "
"x86_64 without KVM. You have three options: 1) Enable KVM 2) "
"Use a 32-bit OS 3) Use another version of qemu.");
#endif
if ( !bootinfo )
{
Panic("The bootinfo structure was NULL. Are your bootloader "