linux-kernel - [PATCH] drm/vmwgfx: Silence RBP clobber warnings

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Date:   Fri,  2 Jun 2023 07:56:34 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Zack Rusin <zackr@...are.com>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Miroslav Benes <mbenes@...e.cz>, x86@...nel.org,
        VMware Graphics Reviewers 
        <linux-graphics-maintainer@...are.com>,
        kernel test robot <lkp@...el.com>
Subject: [PATCH] drm/vmwgfx: Silence RBP clobber warnings

VMware hypercalls take the RBP register as input.  This breaks basic
frame pointer convention, as RBP should never be clobbered.

So frame pointer unwinding is broken for the instructions surrounding
the hypercall with the clobbered RBP.  There's nothing that can be done
about that.  Just tell objtool to ignore it.

Silences the following warnings:

  vmlinux.o: warning: objtool: vmw_port_hb_in+0x1df: return with modified stack frame
  vmlinux.o: warning: objtool: vmw_port_hb_out+0x1dd: return with modified stack frame

Reported-by: kernel test robot <lkp@...el.com>
Link: https://lore.kernel.org/oe-kbuild-all/202305160135.97q0Elax-lkp@intel.com/
Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 arch/x86/include/asm/unwind_hints.h     |  6 ++++++
 drivers/gpu/drm/vmwgfx/vmwgfx_msg_x86.h | 14 ++++++++++----
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/unwind_hints.h b/arch/x86/include/asm/unwind_hints.h
index 01cb9692b160..91ab6e5426c6 100644
--- a/arch/x86/include/asm/unwind_hints.h
+++ b/arch/x86/include/asm/unwind_hints.h
@@ -79,6 +79,12 @@
 #define UNWIND_HINT_FUNC \
 	UNWIND_HINT(UNWIND_HINT_TYPE_FUNC, ORC_REG_SP, 8, 0)
 
+#define UNWIND_HINT_SAVE \
+	UNWIND_HINT(UNWIND_HINT_TYPE_SAVE, 0, 0, 0)
+
+#define UNWIND_HINT_RESTORE \
+	UNWIND_HINT(UNWIND_HINT_TYPE_RESTORE, 0, 0, 0)
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_X86_UNWIND_HINTS_H */
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_msg_x86.h b/drivers/gpu/drm/vmwgfx/vmwgfx_msg_x86.h
index 0b74ca2dfb7b..79050a78fa4c 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_msg_x86.h
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_msg_x86.h
@@ -105,10 +105,13 @@
                         flags, magic, bp,		\
                         eax, ebx, ecx, edx, si, di)	\
 ({							\
-        asm volatile ("push %%rbp;"			\
+        asm volatile (					\
+		UNWIND_HINT_SAVE			\
+		"push %%rbp;"				\
                 "mov %12, %%rbp;"			\
                 VMWARE_HYPERCALL_HB_OUT			\
-                "pop %%rbp;" :				\
+                "pop %%rbp;"				\
+		UNWIND_HINT_RESTORE :			\
                 "=a"(eax),				\
                 "=b"(ebx),				\
                 "=c"(ecx),				\
@@ -130,10 +133,13 @@
                        flags, magic, bp,		\
                        eax, ebx, ecx, edx, si, di)	\
 ({							\
-        asm volatile ("push %%rbp;"			\
+        asm volatile (					\
+		UNWIND_HINT_SAVE			\
+		"push %%rbp;"				\
                 "mov %12, %%rbp;"			\
                 VMWARE_HYPERCALL_HB_IN			\
-                "pop %%rbp" :				\
+                "pop %%rbp;"				\
+		UNWIND_HINT_RESTORE :			\
                 "=a"(eax),				\
                 "=b"(ebx),				\
                 "=c"(ecx),				\
-- 
2.40.1