[Xen-devel] [PATCH v2 1/3] hvmloader/tests: Improvements to shadow_gs_test()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Use .code64 and .code32, and real mnemonics instead of bare opcodes.  No
functional change to the test.

Correct register constraints.  PD_START doesn't necessarily need to be in eax,
but eax does need to identified as clobbered.

As GAS is unable to express a register as an input and also clobbered, opt for
an explicit eax clobber and allow some choice for the register used to pass
PD_START (and indeed, objdump indicates that esi is chosen).  ebx gains an
early clobber to remove it from the candidate list for PD_START.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Keir Fraser <keir@xxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Tim Deegan <tim@xxxxxxx>
CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>

---
v2: Include register constraint fixes as suggested by Jan
---
 tools/firmware/hvmloader/tests.c |   18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/tools/firmware/hvmloader/tests.c b/tools/firmware/hvmloader/tests.c
index 52772aa..931ed2f 100644
--- a/tools/firmware/hvmloader/tests.c
+++ b/tools/firmware/hvmloader/tests.c
@@ -135,7 +135,7 @@ static int rep_io_test(void)
 static int shadow_gs_test(void)
 {
     uint64_t *pd = (uint64_t *)PD_START;
-    uint32_t i, eax, ebx, ecx, edx;
+    uint32_t i, eax, ebx, ecx, edx, dummy;
 
     /* Skip this test if the CPU does not support long mode. */
     cpuid(0x80000000, &eax, &ebx, &ecx, &edx);
@@ -158,7 +158,7 @@ static int shadow_gs_test(void)
         "mov $0x20,%%ebx; "
         "mov %%ebx,%%cr4; "
         /* CR3 */
-        "mov %%eax,%%cr3; "
+        "mov %0,%%cr3; "
         /* EFER.LME=1 */
         "mov $0xc0000080,%%ecx; rdmsr; btsl $8,%%eax; wrmsr; "
         /* CR0.PG=1 */
@@ -170,12 +170,14 @@ static int shadow_gs_test(void)
         /* Push LRETQ stack frame. */
         "pushl $0; pushl $"STR(SEL_CODE32)"; pushl $0; pushl $2f; "
         /* Jump to 64-bit mode. */
-        "ljmp $"STR(SEL_CODE64)",$1f; 1: "
+        "ljmp $"STR(SEL_CODE64)",$1f; "
+        ".code64; 1: "
         /* Swap GS_BASE and SHADOW_GS_BASE */
-        ".byte 0x0f,0x01,0xf8; " /* SWAPGS */
+        "swapgs; "
         /* Jump to 32-bit mode. */
-        ".byte 0x89, 0xe4; "     /* MOV ESP,ESP */
-        ".byte 0x48, 0xcb; 2: "  /* LRETQ */
+        "movl %%esp,%%esp; "
+        "lretq; "
+        ".code32; 2:"
         /* Read SHADOW_GS_BASE: should now contain 2 */
         "mov $0xc0000102,%%ecx; rdmsr; mov %%eax,%%ebx; "
         /* CR0.PG=0 */
@@ -185,7 +187,9 @@ static int shadow_gs_test(void)
         "mov $0xc0000080,%%ecx; rdmsr; btcl $8,%%eax; wrmsr; "
         /* CR4.PAE=0 */
         "xor %%eax,%%eax; mov %%eax,%%cr4; "
-        : "=b" (ebx) : "a" (PD_START) : "ecx", "edx", "memory" );
+        : "=r" (dummy), "=&b" (ebx)
+        : "0" (PD_START)
+        : "eax", "ecx", "edx", "memory" );
 
     return (ebx == 2) ? TEST_PASS : TEST_FAIL;
 }
-- 
1.7.10.4


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