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target/i386: emulate 64-bit ring 0 for linux-user if LM feature is set

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32-bit binaries can run on a long mode processor even if the kernel
is 64-bit, of course, and this can have slightly different behavior;
for example, SYSCALL is allowed on Intel processors.

Allow reporting LM to programs running under user mode emulation,
so that "-cpu" can be used with named CPU models even for qemu-i386
and even without disabling LM by hand.

Fortunately, most of the runtime code in QEMU has to depend on HF_LMA_MASK
or on HF_CS64_MASK (which is anyway false for qemu-i386's 32-bit code
segment) rather than TARGET_X86_64, therefore all that is needed is an
update of linux-user's ring 0 setup.

Fixes: https://gitlab.com/qemu-project/qemu/-/issues/1534
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2023-06-20 16:49:35 +02:00
parent d903259dd2
commit 40a205da41
3 changed files with 44 additions and 34 deletions
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15
target/i386/cpu.c
View file

@ -666,7 +666,10 @@ void x86_cpu_vendor_words2str(char *dst, uint32_t vendor1,
* and therefore using the 32-bit ABI; the CPU itself might be 64-bit
* but again the difference is only visible in kernel mode.
*/
#if defined CONFIG_USER_ONLY
#if defined CONFIG_LINUX_USER
#define CPUID_EXT2_KERNEL_FEATURES (CPUID_EXT2_LM | CPUID_EXT2_FFXSR)
#elif defined CONFIG_USER_ONLY
/* FIXME: Long mode not yet supported for i386 bsd-user */
#define CPUID_EXT2_KERNEL_FEATURES CPUID_EXT2_FFXSR
#else
#define CPUID_EXT2_KERNEL_FEATURES 0
@ -5539,7 +5542,15 @@ uint64_t x86_cpu_get_supported_feature_word(FeatureWord w,
}
#ifndef TARGET_X86_64
if (w == FEAT_8000_0001_EDX) {
r &= ~CPUID_EXT2_LM;
/*
* 32-bit TCG can emulate 64-bit compatibility mode. If there is no
* way for userspace to get out of its 32-bit jail, we can leave
* the LM bit set.
*/
uint32_t unavail = tcg_enabled()
? CPUID_EXT2_LM & ~CPUID_EXT2_KERNEL_FEATURES
: CPUID_EXT2_LM;
r &= ~unavail;
}
#endif
if (migratable_only) {

6
target/i386/tcg/translate.c
View file

@ -173,12 +173,14 @@ typedef struct DisasContext {
#endif
#if !defined(TARGET_X86_64)
#define CODE64(S) false
#define LMA(S) false
#elif defined(CONFIG_USER_ONLY)
#define CODE64(S) true
#define LMA(S) true
#else
#define CODE64(S) (((S)->flags & HF_CS64_MASK) != 0)
#endif
#if defined(CONFIG_SOFTMMU) && !defined(TARGET_X86_64)
#define LMA(S) false
#else
#define LMA(S) (((S)->flags & HF_LMA_MASK) != 0)
#endif