[PATCH 0/2] tcg/riscv64: Fix AUIPC pair range validation

[PATCH 0/2] tcg/riscv64: Fix AUIPC pair range validation

[Max Chou]

This patchset tries to fix the AUIPC-pair range checking issue in
current TCG riscv64 backend.

The issue will be triggered in the following example.
---
Assumptions
- AUIPC at       0x00007fff77fa1258
- target call at 0x00007ffff7fa12d6

The direct pc-relative displacement from the AUIPC at 0x00007fff77fa1258
is 0x000000008000007e, so it is already outside the signed 32-bit range.
tcg_out_call_int therefore takes its far-call path: it separates the JALR
immediate (0x2d6) and asks tcg_out_movi to materialize this page-aligned
base:

  target call  = 0x00007ffff7fa12d6
  JALR lo      =              0x2d6
  base         = 0x00007ffff7fa1000
  base - AUIPC = 0x000000007ffffda8

The final value, 0x7ffffda8, is less than INT32_MAX. The current range 
therefore accepts it, but that is not sufficient: the signed low 12-bit
immediate must be removed before the value can be encoded in AUIPC.

The current reloc_call performs that split as follows:

  int32_t lo = sextreg(offset, 0, 12);
  int32_t hi = offset - lo;

For the captured placement, the values required by the split are:

  offset = 0x000000007ffffda8
  lo     = 0xfffffffffffffda8
  hi     = 0x0000000080000000

The lo is representable by the ADDI immediate. But the hi is not
representable by int32_t: narrowing it produces the bit pattern
0x80000000, which is -0x80000000 as a signed 32-bit value.
Thus the int32_t split can accept a wrapped upper value instead of
proving that the positive upper contribution required by AUIPC is
representable.

AUIPC has a 20-bit immediate which it shifts left by 12 and sign-extends.
Consequently, an encoded immediate of 0x80000 means -0x80000000, not the
required +0x80000000. The resulting generated code will be:

  0x00007fff77fa1258: auipc t6,-524288
  0x00007fff77fa125c: addi  t6,t6,-600
  0x00007fff77fa1260: jalr  ra,t6,726

It computes the base as 0x00007ffef7fa1000 and transfers to
0x00007ffef7fa12d6, exactly 4 GiB below the requested callback which is
0x00007ffff7fa12d6.
---

This patchset addresses the issue of AUIPC split checking and applies
the corrected split. It ensures that the split is checked before
emitting AUIPC/ADDI and AUIPC/JALR pairs in tcg_out_[movi|call_int].

rnax

Max Chou (2):
  tcg/riscv64: Validate AUIPC relocation range
  tcg/riscv64: Fall back when AUIPC pairs are out of range

 tcg/riscv64/tcg-target.c.inc | 68 ++++++++++++++++++++++++++----------
 1 file changed, 49 insertions(+), 19 deletions(-)

-- 
2.43.7

[PATCH 1/2] tcg/riscv64: Validate AUIPC relocation range

[Max Chou]

reloc_call splits a PC-relative offset into a signed 12-bit low
immediate and an AUIPC contribution. When the low immediate carries into
bit 31, the existing 32-bit arithmetic can accept an unencodable
positive 0x80000000 AUIPC contribution.

Keep the split in pointer-width arithmetic and reject it unless the
rounded upper contribution is representable as signed 32-bit. Factor
this validation into split_auipc_offset so reloc_call retains its
existing failure contract.

Fixes: dfa8e74f9463 ("tcg/riscv: Add the relocation functions")
Signed-off-by: Max Chou <max.chou@sifive.com>
---
 tcg/riscv64/tcg-target.c.inc | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/tcg/riscv64/tcg-target.c.inc b/tcg/riscv64/tcg-target.c.inc
index a439ba5c20e..1c41f8ffade 100644
--- a/tcg/riscv64/tcg-target.c.inc
+++ b/tcg/riscv64/tcg-target.c.inc
@@ -634,14 +634,31 @@ static bool reloc_jimm20(tcg_insn_unit *src_rw, const tcg_insn_unit *target)
     return false;
 }
 
-static bool reloc_call(tcg_insn_unit *src_rw, const tcg_insn_unit *target)
+static bool split_auipc_offset(tcg_insn_unit *src_rw,
+                               const tcg_insn_unit *target,
+                               intptr_t *hi, intptr_t *lo)
 {
     const tcg_insn_unit *src_rx = tcg_splitwx_to_rx(src_rw);
     intptr_t offset = (intptr_t)target - (intptr_t)src_rx;
-    int32_t lo = sextreg(offset, 0, 12);
-    int32_t hi = offset - lo;
+    intptr_t low = sextreg(offset, 0, 12);
+    intptr_t high = offset - low;
+
+    /* AUIPC sign-extends its 20-bit immediate after shifting by 12. */
+    if (high != sextreg(high, 0, 32)) {
+        return false;
+    }
+
+    *hi = high;
+    *lo = low;
+
+    return true;
+}
+
+static bool reloc_call(tcg_insn_unit *src_rw, const tcg_insn_unit *target)
+{
+    intptr_t hi, lo;
 
-    if (offset == hi + lo) {
+    if (split_auipc_offset(src_rw, target, &hi, &lo)) {
         src_rw[0] |= encode_uimm20(hi);
         src_rw[1] |= encode_imm12(lo);
         return true;
-- 
2.43.7

[PATCH 2/2] tcg/riscv64: Fall back when AUIPC pairs are out of range

[Max Chou]

tcg_out_movi and tcg_out_call_int only check whether a
PC-relative displacement is signed 32-bit before emitting an AUIPC
pair. This does not account for rounding the signed 12-bit immediate,
which can require an unencodable positive 0x80000000 AUIPC contribution.

Validate the split and emit the pair only when it fits. Otherwise,
tcg_out_movi keeps its existing full-address materialization and
tcg_out_call_int uses its existing indirect far-call sequence.

Fixes: dfa8e74f9463 ("tcg/riscv: Add the relocation functions")
Signed-off-by: Max Chou <max.chou@sifive.com>
---
 tcg/riscv64/tcg-target.c.inc | 43 +++++++++++++++++++++++-------------
 1 file changed, 28 insertions(+), 15 deletions(-)

diff --git a/tcg/riscv64/tcg-target.c.inc b/tcg/riscv64/tcg-target.c.inc
index 1c41f8ffade..12efb44c3d7 100644
--- a/tcg/riscv64/tcg-target.c.inc
+++ b/tcg/riscv64/tcg-target.c.inc
@@ -667,6 +667,21 @@ static bool reloc_call(tcg_insn_unit *src_rw, const tcg_insn_unit *target)
     return false;
 }
 
+static bool tcg_out_auipc_pair(TCGContext *s, const tcg_insn_unit *target,
+                               RISCVInsn opc, TCGReg base,
+                               TCGReg rd, TCGReg rs1)
+{
+    intptr_t hi, lo;
+
+    if (!split_auipc_offset(s->code_ptr, target, &hi, &lo)) {
+        return false;
+    }
+    tcg_out_opc_upper(s, OPC_AUIPC, base, hi);
+    tcg_out_opc_imm(s, opc, rd, rs1, lo);
+
+    return true;
+}
+
 static bool patch_reloc(tcg_insn_unit *code_ptr, int type,
                         intptr_t value, intptr_t addend)
 {
@@ -803,7 +818,8 @@ static void tcg_out_movi(TCGContext *s, TCGType type, TCGReg rd,
                          tcg_target_long val)
 {
     tcg_target_long lo, hi, tmp;
-    int shift, ret;
+    int shift;
+    bool ret;
 
     if (type == TCG_TYPE_I32) {
         val = (int32_t)val;
@@ -824,12 +840,9 @@ static void tcg_out_movi(TCGContext *s, TCGType type, TCGReg rd,
         return;
     }
 
-    tmp = tcg_pcrel_diff(s, (void *)val);
-    if (tmp == (int32_t)tmp) {
-        tcg_out_opc_upper(s, OPC_AUIPC, rd, 0);
-        tcg_out_opc_imm(s, OPC_ADDI, rd, rd, 0);
-        ret = reloc_call(s->code_ptr - 2, (const tcg_insn_unit *)val);
-        tcg_debug_assert(ret == true);
+    ret = tcg_out_auipc_pair(s, (const tcg_insn_unit *)val, OPC_ADDI, rd, rd,
+                             rd);
+    if (ret) {
         return;
     }
 
@@ -1583,7 +1596,7 @@ static void tcg_out_call_int(TCGContext *s, const tcg_insn_unit *arg, bool tail)
 {
     TCGReg link = tail ? TCG_REG_ZERO : TCG_REG_RA;
     ptrdiff_t offset = tcg_pcrel_diff(s, arg);
-    int ret;
+    bool ret;
 
     init_setting_vtype(s);
 
@@ -1591,14 +1604,14 @@ static void tcg_out_call_int(TCGContext *s, const tcg_insn_unit *arg, bool tail)
     if (offset == sextreg(offset, 0, 20)) {
         /* short jump: -2097150 to 2097152 */
         tcg_out_opc_jump(s, OPC_JAL, link, offset);
-    } else if (offset == (int32_t)offset) {
-        /* long jump: -2147483646 to 2147483648 */
-        tcg_out_opc_upper(s, OPC_AUIPC, TCG_REG_TMP0, 0);
-        tcg_out_opc_imm(s, OPC_JALR, link, TCG_REG_TMP0, 0);
-        ret = reloc_call(s->code_ptr - 2, arg);
-        tcg_debug_assert(ret == true);
     } else {
-        /* far jump: 64-bit */
+        ret = tcg_out_auipc_pair(s, arg, OPC_JALR, TCG_REG_TMP0, link,
+                                 TCG_REG_TMP0);
+        if (ret) {
+            return;
+        }
+
+        /* Far jump: 64-bit. */
         tcg_target_long imm = sextreg((tcg_target_long)arg, 0, 12);
         tcg_target_long base = (tcg_target_long)arg - imm;
         tcg_out_movi(s, TCG_TYPE_PTR, TCG_REG_TMP0, base);
-- 
2.43.7

Re: [PATCH 1/2] tcg/riscv64: Validate AUIPC relocation range

[Philippe Mathieu-Daudé]

On 3/9/26 19:04, Max Chou wrote:
> reloc_call splits a PC-relative offset into a signed 12-bit low
> immediate and an AUIPC contribution. When the low immediate carries into
> bit 31, the existing 32-bit arithmetic can accept an unencodable
> positive 0x80000000 AUIPC contribution.
> 
> Keep the split in pointer-width arithmetic and reject it unless the
> rounded upper contribution is representable as signed 32-bit. Factor
> this validation into split_auipc_offset so reloc_call retains its
> existing failure contract.
> 
> Fixes: dfa8e74f9463 ("tcg/riscv: Add the relocation functions")
> Signed-off-by: Max Chou <max.chou@sifive.com>
> ---
>   tcg/riscv64/tcg-target.c.inc | 25 +++++++++++++++++++++----
>   1 file changed, 21 insertions(+), 4 deletions(-)
> 
> diff --git a/tcg/riscv64/tcg-target.c.inc b/tcg/riscv64/tcg-target.c.inc
> index a439ba5c20e..1c41f8ffade 100644
> --- a/tcg/riscv64/tcg-target.c.inc
> +++ b/tcg/riscv64/tcg-target.c.inc
> @@ -634,14 +634,31 @@ static bool reloc_jimm20(tcg_insn_unit *src_rw, const tcg_insn_unit *target)
>       return false;
>   }
>   
> -static bool reloc_call(tcg_insn_unit *src_rw, const tcg_insn_unit *target)
> +static bool split_auipc_offset(tcg_insn_unit *src_rw,
> +                               const tcg_insn_unit *target,
> +                               intptr_t *hi, intptr_t *lo)
>   {
>       const tcg_insn_unit *src_rx = tcg_splitwx_to_rx(src_rw);
>       intptr_t offset = (intptr_t)target - (intptr_t)src_rx;
> -    int32_t lo = sextreg(offset, 0, 12);
> -    int32_t hi = offset - lo;
> +    intptr_t low = sextreg(offset, 0, 12);
> +    intptr_t high = offset - low;
> +
> +    /* AUIPC sign-extends its 20-bit immediate after shifting by 12. */
> +    if (high != sextreg(high, 0, 32)) {
> +        return false;
> +    }
> +
> +    *hi = high;
> +    *lo = low;
> +
> +    return true;
> +}
> +
> +static bool reloc_call(tcg_insn_unit *src_rw, const tcg_insn_unit *target)
> +{
> +    intptr_t hi, lo;
>   
> -    if (offset == hi + lo) {
> +    if (split_auipc_offset(src_rw, target, &hi, &lo)) {
>           src_rw[0] |= encode_uimm20(hi);
>           src_rw[1] |= encode_imm12(lo);

I'm a bit confused by these encode_*imm() taking uint32_t arguments,
otherwise your change LGTM:
Reviewed-by: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>

Re: [PATCH 1/2] tcg/riscv64: Validate AUIPC relocation range

[Max Chou]

On 2026-09-03 19:31, Philippe Mathieu-Daudé wrote:
> > +static bool reloc_call(tcg_insn_unit *src_rw, const tcg_insn_unit *target)
> > +{
> > +    intptr_t hi, lo;
> > -    if (offset == hi + lo) {
> > +    if (split_auipc_offset(src_rw, target, &hi, &lo)) {
> >           src_rw[0] |= encode_uimm20(hi);
> >           src_rw[1] |= encode_imm12(lo);
> 
> I'm a bit confused by these encode_*imm() taking uint32_t arguments,
> otherwise your change LGTM:
> Reviewed-by: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>
> 


Hi Philippe,

Thanks for the feedback.
I’ll address that data type mismatch and send out a v2.

rnax