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authorRich Felker <dalias@libc.org>2015-12-17 01:04:25 +0000
committerRich Felker <dalias@libc.org>2016-03-17 19:46:06 +0000
commit3623d138213aedf0e2c89720f6a3cd0e164cb310 (patch)
tree09dfa5d4a2610f5b1b9b20e964a0ae82e2f64b61
parent940d4113f3306e07a1f86541489b686d1a979d54 (diff)
downloadlinux-sh-3623d138213aedf0e2c89720f6a3cd0e164cb310.tar.gz
sh: provide unified syscall trap compatible with all SH models
Historically SH-2 Linux (and originally uClinux) used a syscall calling convention incompatible with the established SH-3/4 Linux ABI. This choice was made because the trap range used by the existing ABI, 0x10-0x17, overlaps with the hardware exception/interrupt trap range reserved by SH-2, and in particular, with the SH-2A divide-by-zero and division-overflow exceptions. Despite the documented syscall convention using the low bits of the trap number to signal the number of arguments the kernel should expect, no version of the kernel has ever used this information, nor is it useful; all of the registers need to be saved anyway. Therefore, it is possible to pick a new trap number, 0x1f, that is both supported by all existing SH-3/4 kernels and unassigned as a hardware trap in the SH-2 range. This makes it possible to produce SH-2 application binaries that are forwards-compatible with running on SH-3/4 kernels and to treat SH as a unified platform with varying ISA support levels rather than multiple gratuitously-incompatible platforms. This patch adjusts the range checking SH-2 and SH-2A kernels make for the syscall trap to accept the range 0x1f-0x2f rather than just 0x20-0x2f. As a result, trap 0x1f now acts as a syscall for all SH models. Signed-off-by: Rich Felker <dalias@libc.org>
-rw-r--r--arch/sh/kernel/cpu/sh2/entry.S8
-rw-r--r--arch/sh/kernel/cpu/sh2a/entry.S8
-rw-r--r--arch/sh/kernel/entry-common.S21
3 files changed, 23 insertions, 14 deletions
diff --git a/arch/sh/kernel/cpu/sh2/entry.S b/arch/sh/kernel/cpu/sh2/entry.S
index c8a4331d9b8d..a1505956ef28 100644
--- a/arch/sh/kernel/cpu/sh2/entry.S
+++ b/arch/sh/kernel/cpu/sh2/entry.S
@@ -144,9 +144,9 @@ ENTRY(exception_handler)
mov #64,r8
cmp/hs r8,r9
bt interrupt_entry ! vec >= 64 is interrupt
- mov #32,r8
+ mov #31,r8
cmp/hs r8,r9
- bt trap_entry ! 64 > vec >= 32 is trap
+ bt trap_entry ! 64 > vec >= 31 is trap
mov.l 4f,r8
mov r9,r4
@@ -178,9 +178,9 @@ interrupt_entry:
trap_entry:
mov #0x30,r8
- cmp/ge r8,r9 ! vector 0x20-0x2f is systemcall
+ cmp/ge r8,r9 ! vector 0x1f-0x2f is systemcall
bt 1f
- add #-0x10,r9 ! convert SH2 to SH3/4 ABI
+ mov #0x1f,r9 ! convert to unified SH2/3/4 trap number
1:
shll2 r9 ! TRA
bra system_call ! jump common systemcall entry
diff --git a/arch/sh/kernel/cpu/sh2a/entry.S b/arch/sh/kernel/cpu/sh2a/entry.S
index 222742ddc0d6..da77a8ef4696 100644
--- a/arch/sh/kernel/cpu/sh2a/entry.S
+++ b/arch/sh/kernel/cpu/sh2a/entry.S
@@ -109,9 +109,9 @@ ENTRY(exception_handler)
mov #64,r8
cmp/hs r8,r9
bt interrupt_entry ! vec >= 64 is interrupt
- mov #32,r8
+ mov #31,r8
cmp/hs r8,r9
- bt trap_entry ! 64 > vec >= 32 is trap
+ bt trap_entry ! 64 > vec >= 31 is trap
mov.l 4f,r8
mov r9,r4
@@ -143,9 +143,9 @@ interrupt_entry:
trap_entry:
mov #0x30,r8
- cmp/ge r8,r9 ! vector 0x20-0x2f is systemcall
+ cmp/ge r8,r9 ! vector 0x1f-0x2f is systemcall
bt 1f
- add #-0x10,r9 ! convert SH2 to SH3/4 ABI
+ mov #0x1f,r9 ! convert to unified SH2/3/4 trap number
1:
shll2 r9 ! TRA
bra system_call ! jump common systemcall entry
diff --git a/arch/sh/kernel/entry-common.S b/arch/sh/kernel/entry-common.S
index 13047a4facd2..c001f782c5f1 100644
--- a/arch/sh/kernel/entry-common.S
+++ b/arch/sh/kernel/entry-common.S
@@ -268,20 +268,29 @@ debug_trap:
* Syscall #: R3
* Arguments #0 to #3: R4--R7
* Arguments #4 to #6: R0, R1, R2
- * TRA: (number of arguments + ABI revision) x 4
+ * TRA: See following table.
*
- * This code also handles delegating other traps to the BIOS/gdb stub
- * according to:
- *
- * Trap number
* (TRA>>2) Purpose
* -------- -------
* 0x00-0x0f original SH-3/4 syscall ABI (not in general use).
* 0x10-0x1f general SH-3/4 syscall ABI.
- * 0x20-0x2f syscall ABI for SH-2 parts.
+ * 0x1f unified SH-2/3/4 syscall ABI (preferred).
+ * 0x20-0x2f original SH-2 syscall ABI.
* 0x30-0x3f debug traps used by the kernel.
* 0x40-0xff Not supported by all parts, so left unhandled.
*
+ * For making system calls, any trap number in the range for the
+ * given cpu model may be used, but the unified trap number 0x1f is
+ * preferred for compatibility with all models.
+ *
+ * The low bits of the trap number were once documented as matching
+ * the number of arguments, but they were never actually used as such
+ * by the kernel. SH-2 originally used its own separate trap range
+ * because several hardware exceptions fell in the range used for the
+ * SH-3/4 syscall ABI.
+ *
+ * This code also handles delegating other traps to the BIOS/gdb stub.
+ *
* Note: When we're first called, the TRA value must be shifted
* right 2 bits in order to get the value that was used as the "trapa"
* argument.