[RFC PATCH v2 4/5] arm64: Support for Static Trampolines
madvenka@linux.microsoft.com
madvenka@linux.microsoft.com
Wed Dec 16 19:40:08 GMT 2020
From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
- Define the arch-specific initialization function ffi_tramp_arch ()
that returns trampoline size information to common code.
- Define the trampoline code mapping and data mapping sizes.
- Define the trampoline code table statically.
- Introduce a tiny prolog for each ABI handling function. The ABI
handlers addressed are:
- ffi_closure_SYSV
- ffi_closure_SYSV_V
Their prolog functions are called:
- ffi_closure_SYSV_alt
- ffi_closure_SYSV_V_alt
The legacy trampoline jumps to the ABI handler. The static
trampoline jumps to the prolog function. The prolog function uses
the information provided by the static trampoline, sets things up
for the ABI handler and then jumps to the ABI handler.
- Call ffi_closure_tramp_init () in ffi_prep_closure_loc () to
initialize static trampoline parameters.
Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
---
src/aarch64/ffi.c | 36 ++++++++++++++++++++++--
src/aarch64/internal.h | 10 +++++++
src/aarch64/sysv.S | 64 ++++++++++++++++++++++++++++++++++++++++++
3 files changed, 107 insertions(+), 3 deletions(-)
diff --git a/src/aarch64/ffi.c b/src/aarch64/ffi.c
index ef09f4d..0d7d8ac 100644
--- a/src/aarch64/ffi.c
+++ b/src/aarch64/ffi.c
@@ -781,7 +781,9 @@ ffi_call_go (ffi_cif *cif, void (*fn) (void), void *rvalue,
/* Build a trampoline. */
extern void ffi_closure_SYSV (void) FFI_HIDDEN;
+extern void ffi_closure_SYSV_alt (void) FFI_HIDDEN;
extern void ffi_closure_SYSV_V (void) FFI_HIDDEN;
+extern void ffi_closure_SYSV_V_alt (void) FFI_HIDDEN;
ffi_status
ffi_prep_closure_loc (ffi_closure *closure,
@@ -794,11 +796,18 @@ ffi_prep_closure_loc (ffi_closure *closure,
return FFI_BAD_ABI;
void (*start)(void);
+ void (*start_alt)(void);
if (cif->flags & AARCH64_FLAG_ARG_V)
- start = ffi_closure_SYSV_V;
+ {
+ start = ffi_closure_SYSV_V;
+ start_alt = ffi_closure_SYSV_V_alt;
+ }
else
- start = ffi_closure_SYSV;
+ {
+ start = ffi_closure_SYSV;
+ start_alt = ffi_closure_SYSV_alt;
+ }
#if FFI_EXEC_TRAMPOLINE_TABLE
#ifdef __MACH__
@@ -816,7 +825,15 @@ ffi_prep_closure_loc (ffi_closure *closure,
0x00, 0x02, 0x1f, 0xd6 /* br x16 */
};
char *tramp = closure->tramp;
-
+
+ if (ffi_tramp_is_present(closure))
+ {
+ /* Initialize the static trampoline's parameters. */
+ ffi_tramp_set_parms (closure->ftramp, start_alt, closure);
+ goto out;
+ }
+
+ /* Initialize the dynamic trampoline. */
memcpy (tramp, trampoline, sizeof(trampoline));
*(UINT64 *)(tramp + 16) = (uintptr_t)start;
@@ -832,6 +849,7 @@ ffi_prep_closure_loc (ffi_closure *closure,
unsigned char *tramp_code = ffi_data_to_code_pointer (tramp);
#endif
ffi_clear_cache (tramp_code, tramp_code + FFI_TRAMPOLINE_SIZE);
+out:
#endif
closure->cif = cif;
@@ -1022,4 +1040,16 @@ ffi_closure_SYSV_inner (ffi_cif *cif,
return flags;
}
+#if defined(FFI_EXEC_STATIC_TRAMP)
+void *
+ffi_tramp_arch (size_t *tramp_size, size_t *map_size)
+{
+ extern void *trampoline_code_table;
+
+ *tramp_size = AARCH64_TRAMP_SIZE;
+ *map_size = AARCH64_TRAMP_MAP_SIZE;
+ return &trampoline_code_table;
+}
+#endif
+
#endif /* (__aarch64__) || defined(__arm64__)|| defined (_M_ARM64)*/
diff --git a/src/aarch64/internal.h b/src/aarch64/internal.h
index 3d4d035..de55755 100644
--- a/src/aarch64/internal.h
+++ b/src/aarch64/internal.h
@@ -66,3 +66,13 @@ SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */
#define N_X_ARG_REG 8
#define N_V_ARG_REG 8
#define CALL_CONTEXT_SIZE (N_V_ARG_REG * 16 + N_X_ARG_REG * 8)
+
+#if defined(FFI_EXEC_STATIC_TRAMP)
+/*
+ * For the trampoline code table mapping, a mapping size of 16K is chosen to
+ * cover the base page sizes of 4K and 16K.
+ */
+#define AARCH64_TRAMP_MAP_SHIFT 14
+#define AARCH64_TRAMP_MAP_SIZE (1 << AARCH64_TRAMP_MAP_SHIFT)
+#define AARCH64_TRAMP_SIZE 32
+#endif
diff --git a/src/aarch64/sysv.S b/src/aarch64/sysv.S
index b720a92..6c39cdc 100644
--- a/src/aarch64/sysv.S
+++ b/src/aarch64/sysv.S
@@ -252,6 +252,19 @@ CNAME(ffi_closure_SYSV_V):
.size CNAME(ffi_closure_SYSV_V), . - CNAME(ffi_closure_SYSV_V)
#endif
+ .align 4
+CNAME(ffi_closure_SYSV_V_alt):
+ ldr x17, [sp, #8]
+ add sp, sp, #16
+ b CNAME(ffi_closure_SYSV_V)
+
+ .globl CNAME(ffi_closure_SYSV_V_alt)
+ FFI_HIDDEN(CNAME(ffi_closure_SYSV_V_alt))
+#ifdef __ELF__
+ .type CNAME(ffi_closure_SYSV_V_alt), #function
+ .size CNAME(ffi_closure_SYSV_V_alt), . - CNAME(ffi_closure_SYSV_V_alt)
+#endif
+
.align 4
cfi_startproc
CNAME(ffi_closure_SYSV):
@@ -367,6 +380,57 @@ CNAME(ffi_closure_SYSV):
.size CNAME(ffi_closure_SYSV), . - CNAME(ffi_closure_SYSV)
#endif
+ .align 4
+CNAME(ffi_closure_SYSV_alt):
+ ldr x17, [sp, #8]
+ add sp, sp, #16
+ b CNAME(ffi_closure_SYSV)
+
+ .globl CNAME(ffi_closure_SYSV_alt)
+ FFI_HIDDEN(CNAME(ffi_closure_SYSV_alt))
+#ifdef __ELF__
+ .type CNAME(ffi_closure_SYSV_alt), #function
+ .size CNAME(ffi_closure_SYSV_alt), . - CNAME(ffi_closure_SYSV_alt)
+#endif
+
+#if defined(FFI_EXEC_STATIC_TRAMP)
+/*
+ * The trampoline uses register x17. It saves the original value of x17 on
+ * the stack.
+ *
+ * The trampoline has two parameters - target code to jump to and data for
+ * the target code. The trampoline extracts the parameters from its parameter
+ * block (see tramp_table_map()). The trampoline saves the data address on
+ * the stack. Finally, it jumps to the target code.
+ *
+ * The target code can choose to:
+ *
+ * - restore the value of x17
+ * - load the data address in a register
+ * - restore the stack pointer to what it was when the trampoline was invoked.
+ */
+ .align AARCH64_TRAMP_MAP_SHIFT
+CNAME(trampoline_code_table):
+ .rept AARCH64_TRAMP_MAP_SIZE / AARCH64_TRAMP_SIZE
+ sub sp, sp, #16 /* Make space on the stack */
+ str x17, [sp] /* Save x17 on stack */
+ adr x17, #16376 /* Get data address */
+ ldr x17, [x17] /* Copy data into x17 */
+ str x17, [sp, #8] /* Save data on stack */
+ adr x17, #16372 /* Get code address */
+ ldr x17, [x17] /* Load code address into x17 */
+ br x17 /* Jump to code */
+ .endr
+
+ .globl CNAME(trampoline_code_table)
+ FFI_HIDDEN(CNAME(trampoline_code_table))
+#ifdef __ELF__
+ .type CNAME(trampoline_code_table), #function
+ .size CNAME(trampoline_code_table), . - CNAME(trampoline_code_table)
+#endif
+ .align AARCH64_TRAMP_MAP_SHIFT
+#endif /* FFI_EXEC_STATIC_TRAMP */
+
#if FFI_EXEC_TRAMPOLINE_TABLE
#ifdef __MACH__
--
2.27.0
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