[PATCH 2/9] x86/extable: switch to using FIELD_GET_SIGNED()

[Yury Norov]

The EX_DATA register is laid out such that EX_DATA_IMM occupied MSB.
It's done to make sure that FIELD_GET() will sign-extend the IMM
field during extraction.

To enforce that, all EX_DATA masks are made signed integers. This
works, but relies on the particular implementation of FIELD_GET(),
i.e. masking then shifting, not vice versa; and the particular
placement of the fields in the register.

Switch to using the dedicated FIELD_GET_SIGNED(), and relax those
limitations.

Signed-off-by: Yury Norov <ynorov@xxxxxxxxxx>
---
 arch/x86/include/asm/extable_fixup_types.h | 13 ++++---------
 arch/x86/mm/extable.c                      |  2 +-
 2 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/extable_fixup_types.h b/arch/x86/include/asm/extable_fixup_types.h
index 906b0d5541e8..fd0cfb472103 100644
--- a/arch/x86/include/asm/extable_fixup_types.h
+++ b/arch/x86/include/asm/extable_fixup_types.h
@@ -2,15 +2,10 @@
 #ifndef _ASM_X86_EXTABLE_FIXUP_TYPES_H
 #define _ASM_X86_EXTABLE_FIXUP_TYPES_H
 
-/*
- * Our IMM is signed, as such it must live at the top end of the word. Also,
- * since C99 hex constants are of ambiguous type, force cast the mask to 'int'
- * so that FIELD_GET() will DTRT and sign extend the value when it extracts it.
- */
-#define EX_DATA_TYPE_MASK		((int)0x000000FF)
-#define EX_DATA_REG_MASK		((int)0x00000F00)
-#define EX_DATA_FLAG_MASK		((int)0x0000F000)
-#define EX_DATA_IMM_MASK		((int)0xFFFF0000)
+#define EX_DATA_TYPE_MASK		(0x000000FF)
+#define EX_DATA_REG_MASK		(0x00000F00)
+#define EX_DATA_FLAG_MASK		(0x0000F000)
+#define EX_DATA_IMM_MASK		(0xFFFF0000)
 
 #define EX_DATA_REG_SHIFT		8
 #define EX_DATA_FLAG_SHIFT		12
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 6b9ff1c6cafa..ae663cf88a3c 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -322,7 +322,7 @@ int fixup_exception(struct pt_regs *regs, int trapnr, unsigned long error_code,
 
 	type = FIELD_GET(EX_DATA_TYPE_MASK, e->data);
 	reg  = FIELD_GET(EX_DATA_REG_MASK,  e->data);
-	imm  = FIELD_GET(EX_DATA_IMM_MASK,  e->data);
+	imm  = FIELD_GET_SIGNED(EX_DATA_IMM_MASK, e->data);
 
 	switch (type) {
 	case EX_TYPE_DEFAULT:
-- 
2.51.0