[Qemu-devel] [PATCH v2 0/3] Relax code buffer size limitation on aarch64 hosts

[Qemu-devel] [PATCH v2 0/3] Relax code buffer size limitation on aarch64 hosts

[Pranith Kumar]

Hello,

The following patches enable us to relax the 128MB code buffer size
limitation on ARM64 hosts.

Patch 2 increases this limitation to 3GB, even though ADRP+ADD can
address 4GB of pc-relative addresses to give us some slack.

Patch 3 uses LDR (literal) to load the address, allowing us to remove
the code buffer size limitation altogether. However, I feel that 3GB
should be sufficient for now and hence did not change it ;). It
however enables the !USE_DIRECT_JUMP path on aarch64 hosts.

Thanks,

Pranith Kumar (3):
  tcg/aarch64: Introduce and use long branch to register
  tcg/aarch64: Use ADRP+ADD to compute target address
  tcg/aarch64: Enable indirect jump path using LDR (literal)

 accel/tcg/translate-all.c    |  2 +-
 tcg/aarch64/tcg-target.inc.c | 69 +++++++++++++++++++++++++++++++++++---------
 2 files changed, 56 insertions(+), 15 deletions(-)

-- 
2.13.0

[Qemu-devel] [PATCH v2 1/3] tcg/aarch64: Introduce and use long branch to register

[Pranith Kumar]

We can use a branch to register instruction for exit_tb for offsets
greater than 128MB.

CC: Richard Henderson <rth@twiddle.net>
CC: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
---
 tcg/aarch64/tcg-target.inc.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/tcg/aarch64/tcg-target.inc.c b/tcg/aarch64/tcg-target.inc.c
index 1fa3bccc89..8fce11ace7 100644
--- a/tcg/aarch64/tcg-target.inc.c
+++ b/tcg/aarch64/tcg-target.inc.c
@@ -819,6 +819,17 @@ static inline void tcg_out_goto(TCGContext *s, tcg_insn_unit *target)
     tcg_out_insn(s, 3206, B, offset);
 }
 
+static inline void tcg_out_goto_long(TCGContext *s, tcg_insn_unit *target)
+{
+    ptrdiff_t offset = target - s->code_ptr;
+    if (offset == sextract64(offset, 0, 26)) {
+        tcg_out_insn(s, 3206, BL, offset);
+    } else {
+        tcg_out_movi(s, TCG_TYPE_I64, TCG_REG_TMP, (intptr_t)target);
+        tcg_out_insn(s, 3207, BR, TCG_REG_TMP);
+    }
+}
+
 static inline void tcg_out_goto_noaddr(TCGContext *s)
 {
     /* We pay attention here to not modify the branch target by reading from
@@ -1364,10 +1375,10 @@ static void tcg_out_op(TCGContext *s, TCGOpcode opc,
     case INDEX_op_exit_tb:
         /* Reuse the zeroing that exists for goto_ptr.  */
         if (a0 == 0) {
-            tcg_out_goto(s, s->code_gen_epilogue);
+            tcg_out_goto_long(s, s->code_gen_epilogue);
         } else {
             tcg_out_movi(s, TCG_TYPE_I64, TCG_REG_X0, a0);
-            tcg_out_goto(s, tb_ret_addr);
+            tcg_out_goto_long(s, tb_ret_addr);
         }
         break;
 
-- 
2.13.0

Re: [Qemu-devel] [PATCH v2 1/3] tcg/aarch64: Introduce and use long branch to register

[Richard Henderson]

On 06/29/2017 12:52 AM, Pranith Kumar wrote:
> We can use a branch to register instruction for exit_tb for offsets
> greater than 128MB.
> 
> CC: Richard Henderson<rth@twiddle.net>
> CC: Alex Bennée<alex.bennee@linaro.org>
> Signed-off-by: Pranith Kumar<bobby.prani@gmail.com>
> ---
>   tcg/aarch64/tcg-target.inc.c | 15 +++++++++++++--
>   1 file changed, 13 insertions(+), 2 deletions(-)

Reviewed-by: Richard Henderson <rth@twiddle.net>


r~

[Qemu-devel] [PATCH v2 2/3] tcg/aarch64: Use ADRP+ADD to compute target address

[Pranith Kumar]

We use ADRP+ADD to compute the target address for goto_tb. This patch
introduces the NOP instruction which is used to align the above
instruction pair so that we can use one atomic instruction to patch
the destination offsets.

CC: Richard Henderson <rth@twiddle.net>
CC: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
---
 accel/tcg/translate-all.c    |  2 +-
 tcg/aarch64/tcg-target.inc.c | 26 +++++++++++++++++++++-----
 2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
index f6ad46b613..b6d122e087 100644
--- a/accel/tcg/translate-all.c
+++ b/accel/tcg/translate-all.c
@@ -522,7 +522,7 @@ static inline PageDesc *page_find(tb_page_addr_t index)
 #elif defined(__powerpc__)
 # define MAX_CODE_GEN_BUFFER_SIZE  (32u * 1024 * 1024)
 #elif defined(__aarch64__)
-# define MAX_CODE_GEN_BUFFER_SIZE  (128ul * 1024 * 1024)
+# define MAX_CODE_GEN_BUFFER_SIZE  (3ul * 1024 * 1024 * 1024)
 #elif defined(__s390x__)
   /* We have a +- 4GB range on the branches; leave some slop.  */
 # define MAX_CODE_GEN_BUFFER_SIZE  (3ul * 1024 * 1024 * 1024)
diff --git a/tcg/aarch64/tcg-target.inc.c b/tcg/aarch64/tcg-target.inc.c
index 8fce11ace7..b7670ecc90 100644
--- a/tcg/aarch64/tcg-target.inc.c
+++ b/tcg/aarch64/tcg-target.inc.c
@@ -372,6 +372,7 @@ typedef enum {
     I3510_EON       = 0x4a200000,
     I3510_ANDS      = 0x6a000000,
 
+    NOP             = 0xd503201f,
     /* System instructions.  */
     DMB_ISH         = 0xd50338bf,
     DMB_LD          = 0x00000100,
@@ -866,10 +867,18 @@ static inline void tcg_out_call(TCGContext *s, tcg_insn_unit *target)
 void aarch64_tb_set_jmp_target(uintptr_t jmp_addr, uintptr_t addr)
 {
     tcg_insn_unit *code_ptr = (tcg_insn_unit *)jmp_addr;
-    tcg_insn_unit *target = (tcg_insn_unit *)addr;
+    tcg_insn_unit adrp_insn = *code_ptr++;
+    tcg_insn_unit addi_insn = *code_ptr;
 
-    reloc_pc26_atomic(code_ptr, target);
-    flush_icache_range(jmp_addr, jmp_addr + 4);
+    ptrdiff_t offset = (addr >> 12) - (jmp_addr >> 12);
+
+    /* patch ADRP */
+    adrp_insn = deposit32(adrp_insn, 29, 2, offset & 0x3);
+    adrp_insn = deposit32(adrp_insn, 5, 19, offset >> 2);
+    /* patch ADDI */
+    addi_insn = deposit32(addi_insn, 10, 12, addr & 0xfff);
+    atomic_set((uint64_t *)jmp_addr, adrp_insn | ((uint64_t)addi_insn << 32));
+    flush_icache_range(jmp_addr, jmp_addr + 8);
 }
 
 static inline void tcg_out_goto_label(TCGContext *s, TCGLabel *l)
@@ -1388,10 +1397,17 @@ static void tcg_out_op(TCGContext *s, TCGOpcode opc,
 #endif
         /* consistency for USE_DIRECT_JUMP */
         tcg_debug_assert(s->tb_jmp_insn_offset != NULL);
+        /* Ensure that ADRP+ADD are 8-byte aligned so that an atomic
+           write can be used to patch the target address. */
+        if ((uintptr_t)s->code_ptr & 7) {
+            tcg_out32(s, NOP);
+        }
         s->tb_jmp_insn_offset[a0] = tcg_current_code_size(s);
         /* actual branch destination will be patched by
-           aarch64_tb_set_jmp_target later, beware retranslation. */
-        tcg_out_goto_noaddr(s);
+           aarch64_tb_set_jmp_target later, beware of retranslation */
+        tcg_out_insn(s, 3406, ADRP, TCG_REG_TMP, 0);
+        tcg_out_insn(s, 3401, ADDI, TCG_TYPE_I64, TCG_REG_TMP, TCG_REG_TMP, 0);
+        tcg_out_callr(s, TCG_REG_TMP);
         s->tb_jmp_reset_offset[a0] = tcg_current_code_size(s);
         break;
 
-- 
2.13.0

Re: [Qemu-devel] [PATCH v2 2/3] tcg/aarch64: Use ADRP+ADD to compute target address

[Richard Henderson]

On 06/29/2017 12:52 AM, Pranith Kumar wrote:
> We use ADRP+ADD to compute the target address for goto_tb. This patch
> introduces the NOP instruction which is used to align the above
> instruction pair so that we can use one atomic instruction to patch
> the destination offsets.
> 
> CC: Richard Henderson <rth@twiddle.net>
> CC: Alex Bennée <alex.bennee@linaro.org>
> Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
> ---
>   accel/tcg/translate-all.c    |  2 +-
>   tcg/aarch64/tcg-target.inc.c | 26 +++++++++++++++++++++-----
>   2 files changed, 22 insertions(+), 6 deletions(-)
> 
> diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
> index f6ad46b613..b6d122e087 100644
> --- a/accel/tcg/translate-all.c
> +++ b/accel/tcg/translate-all.c
> @@ -522,7 +522,7 @@ static inline PageDesc *page_find(tb_page_addr_t index)
>   #elif defined(__powerpc__)
>   # define MAX_CODE_GEN_BUFFER_SIZE  (32u * 1024 * 1024)
>   #elif defined(__aarch64__)
> -# define MAX_CODE_GEN_BUFFER_SIZE  (128ul * 1024 * 1024)
> +# define MAX_CODE_GEN_BUFFER_SIZE  (3ul * 1024 * 1024 * 1024)

The max is 2GB, because the 4GB range of ADRP is signed.
The end of the buffer must be able to address the beginning of the buffer.

>   void aarch64_tb_set_jmp_target(uintptr_t jmp_addr, uintptr_t addr)
>   {
>       tcg_insn_unit *code_ptr = (tcg_insn_unit *)jmp_addr;
> -    tcg_insn_unit *target = (tcg_insn_unit *)addr;
> +    tcg_insn_unit adrp_insn = *code_ptr++;
> +    tcg_insn_unit addi_insn = *code_ptr;
>   
> -    reloc_pc26_atomic(code_ptr, target);
> -    flush_icache_range(jmp_addr, jmp_addr + 4);
> +    ptrdiff_t offset = (addr >> 12) - (jmp_addr >> 12);
> +
> +    /* patch ADRP */
> +    adrp_insn = deposit32(adrp_insn, 29, 2, offset & 0x3);
> +    adrp_insn = deposit32(adrp_insn, 5, 19, offset >> 2);
> +    /* patch ADDI */
> +    addi_insn = deposit32(addi_insn, 10, 12, addr & 0xfff);
> +    atomic_set((uint64_t *)jmp_addr, adrp_insn | ((uint64_t)addi_insn << 32));
> +    flush_icache_range(jmp_addr, jmp_addr + 8);

(1) You don't need to load the ADRP and ADDI insns, because you know exactly 
what they are.  (2) You should check to see if the branch is within 128MB and 
use a direct branch in that case; it will happen quite often.  See the ppc64 
ppc_tb_set_jmp_target for an example.

>           /* actual branch destination will be patched by
> +           aarch64_tb_set_jmp_target later, beware of retranslation */

We can actually drop the retranslation comment now; that's a cleanup that 
should be applied to all of the backends...

> +        tcg_out_insn(s, 3406, ADRP, TCG_REG_TMP, 0);
> +        tcg_out_insn(s, 3401, ADDI, TCG_TYPE_I64, TCG_REG_TMP, TCG_REG_TMP, 0);
> +        tcg_out_callr(s, TCG_REG_TMP);

Don't use callr, use BR like you did for goto_long in the previous patch.


r~

[Qemu-devel] [PATCH v3 3/3] tcg/aarch64: Enable indirect jump path using LDR (literal)

[Pranith Kumar]

This patch enables the indirect jump path using an LDR (literal)
instruction. It will be interesting to test and see which performs
better among the two paths.

CC: Richard Henderson <rth@twiddle.net>
CC: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
---
 tcg/aarch64/tcg-target.inc.c | 42 ++++++++++++++++++++++++++++--------------
 1 file changed, 28 insertions(+), 14 deletions(-)

diff --git a/tcg/aarch64/tcg-target.inc.c b/tcg/aarch64/tcg-target.inc.c
index b7670ecc90..5381c31b45 100644
--- a/tcg/aarch64/tcg-target.inc.c
+++ b/tcg/aarch64/tcg-target.inc.c
@@ -269,6 +269,8 @@ typedef enum {
     I3207_BLR       = 0xd63f0000,
     I3207_RET       = 0xd65f0000,
 
+    /* Load literal for loading the address at pc-relative offset */
+    I3305_LDR       = 0x58000000,
     /* Load/store register.  Described here as 3.3.12, but the helper
        that emits them can transform to 3.3.10 or 3.3.13.  */
     I3312_STRB      = 0x38000000 | LDST_ST << 22 | MO_8 << 30,
@@ -389,6 +391,11 @@ static inline uint32_t tcg_in32(TCGContext *s)
 #define tcg_out_insn(S, FMT, OP, ...) \
     glue(tcg_out_insn_,FMT)(S, glue(glue(glue(I,FMT),_),OP), ## __VA_ARGS__)
 
+static void tcg_out_insn_3305(TCGContext *s, AArch64Insn insn, int imm19, TCGReg rt)
+{
+    tcg_out32(s, insn | (imm19 & 0x7ffff) << 5 | rt);
+}
+
 static void tcg_out_insn_3201(TCGContext *s, AArch64Insn insn, TCGType ext,
                               TCGReg rt, int imm19)
 {
@@ -864,6 +871,8 @@ static inline void tcg_out_call(TCGContext *s, tcg_insn_unit *target)
     }
 }
 
+#ifdef USE_DIRECT_JUMP
+
 void aarch64_tb_set_jmp_target(uintptr_t jmp_addr, uintptr_t addr)
 {
     tcg_insn_unit *code_ptr = (tcg_insn_unit *)jmp_addr;
@@ -881,6 +890,8 @@ void aarch64_tb_set_jmp_target(uintptr_t jmp_addr, uintptr_t addr)
     flush_icache_range(jmp_addr, jmp_addr + 8);
 }
 
+#endif
+
 static inline void tcg_out_goto_label(TCGContext *s, TCGLabel *l)
 {
     if (!l->has_value) {
@@ -1392,21 +1403,24 @@ static void tcg_out_op(TCGContext *s, TCGOpcode opc,
         break;
 
     case INDEX_op_goto_tb:
-#ifndef USE_DIRECT_JUMP
-#error "USE_DIRECT_JUMP required for aarch64"
-#endif
-        /* consistency for USE_DIRECT_JUMP */
-        tcg_debug_assert(s->tb_jmp_insn_offset != NULL);
-        /* Ensure that ADRP+ADD are 8-byte aligned so that an atomic
-           write can be used to patch the target address. */
-        if ((uintptr_t)s->code_ptr & 7) {
-            tcg_out32(s, NOP);
+        if (s->tb_jmp_insn_offset != NULL) {
+            /* USE_DIRECT_JUMP */
+            /* Ensure that ADRP+ADD are 8-byte aligned so that an atomic
+               write can be used to patch the target address. */
+            if ((uintptr_t)s->code_ptr & 7) {
+                tcg_out32(s, NOP);
+            }
+            s->tb_jmp_insn_offset[a0] = tcg_current_code_size(s);
+            /* actual branch destination will be patched by
+               aarch64_tb_set_jmp_target later, beware of retranslation */
+            tcg_out_insn(s, 3406, ADRP, TCG_REG_TMP, 0);
+            tcg_out_insn(s, 3401, ADDI, TCG_TYPE_I64, TCG_REG_TMP, TCG_REG_TMP, 0);
+        } else {
+            /* !USE_DIRECT_JUMP */
+            tcg_debug_assert(s->tb_jmp_target_addr != NULL);
+            intptr_t offset = tcg_pcrel_diff(s, (s->tb_jmp_target_addr + a0)) >> 2;
+            tcg_out_insn(s, 3305, LDR, offset, TCG_REG_TMP);
         }
-        s->tb_jmp_insn_offset[a0] = tcg_current_code_size(s);
-        /* actual branch destination will be patched by
-           aarch64_tb_set_jmp_target later, beware of retranslation */
-        tcg_out_insn(s, 3406, ADRP, TCG_REG_TMP, 0);
-        tcg_out_insn(s, 3401, ADDI, TCG_TYPE_I64, TCG_REG_TMP, TCG_REG_TMP, 0);
         tcg_out_callr(s, TCG_REG_TMP);
         s->tb_jmp_reset_offset[a0] = tcg_current_code_size(s);
         break;
-- 
2.13.0

Re: [Qemu-devel] [PATCH v3 3/3] tcg/aarch64: Enable indirect jump path using LDR (literal)

[Richard Henderson]

On 06/29/2017 12:52 AM, Pranith Kumar wrote:
> This patch enables the indirect jump path using an LDR (literal)
> instruction. It will be interesting to test and see which performs
> better among the two paths.
> 
> CC: Richard Henderson<rth@twiddle.net>
> CC: Alex Bennée<alex.bennee@linaro.org>
> Signed-off-by: Pranith Kumar<bobby.prani@gmail.com>
> ---
>   tcg/aarch64/tcg-target.inc.c | 42 ++++++++++++++++++++++++++++--------------
>   1 file changed, 28 insertions(+), 14 deletions(-)

Reviewed-by: Richard Henderson <rth@twiddle.net>


r~