Re: [PATCH v2 63/93] tcg/tci: Use ffi for calls

[Richard Henderson]

On 2/8/21 2:55 PM, Richard Henderson wrote:
> Ok, I've reproduced something on a T3 (gcc102.fsffrance.org).
> Running the same code side-by-side vs the T5, I get different results.

Brown paper bag time: the T5 build dir lost the --enable-tcg-interpreter flag,
so was testing tcg native.

Big-endian bug wrt an odd api wart in libffi.  Fixed thus.


r~

diff --git a/tcg/tci.c b/tcg/tci.c
index d27db9f720..dd0cca296a 100644
--- a/tcg/tci.c
+++ b/tcg/tci.c
@@ -557,8 +557,15 @@ uintptr_t QEMU_DISABLE_CFI tcg_qemu_tb_exec(CPUArchState *env,
             case 0: /* void */
                 break;
             case 1: /* uint32_t */
-                regs[TCG_REG_R0] = *(uint32_t *)stack;
-                break;
+                /*
+                 * Note that libffi has an odd special case in that it will
+                 * always widen an integral result to ffi_arg.
+                 */
+                if (sizeof(ffi_arg) == 4) {
+                    regs[TCG_REG_R0] = *(uint32_t *)stack;
+                    break;
+                }
+                /* fall through */
             case 2: /* uint64_t */
                 if (TCG_TARGET_REG_BITS == 32) {
                     tci_write_reg64(regs, TCG_REG_R1, TCG_REG_R0, stack[0]);