[PATCH v2 1/1] target/ppc: fix unreachable code in do_ldst_quad()

[Daniel Henrique Barboza <danielhb413@gmail.com>]

Coverity reports that commit fc34e81acd51 ("target/ppc: add macros to
check privilege level") turned the following code unreachable:

if (!prefixed && !(ctx->insns_flags2 & PPC2_LSQ_ISA207)) {
    /* lq and stq were privileged prior to V. 2.07 */
    REQUIRE_SV(ctx);

>>>     CID 1490757:  Control flow issues  (UNREACHABLE)
>>>     This code cannot be reached: "if (ctx->le_mode) {
    if (ctx->le_mode) {
        gen_align_no_le(ctx);
        return true;
    }
}

This happens because the macro REQUIRE_SV(), in CONFIG_USER_MODE, will
always result in a 'return true' statement. In fact, all REQUIRE_*
macros for target/ppc/translate.c behave the same way: if a condition
isn't met, an exception is generated and a 'return' statement is issued.

The difference is that all other callers are using it in insns that are
not implemented in user mode. do_ldst_quad(), on the other hand, is user
mode compatible.

Fixes include wrapping these lines in "if !defined(CONFIG_USER_MODE)",
making it explicit that these lines are not user mode anymore. Another
fix would be, for example, to change REQUIRE_SV() to not issue a
'return' and check if we're running in privileged mode or not by hand,
but this would change all other callers of the macro that are using it
in an adequate manner.

The code that was in place before fc34e81acd51 was good enough, so let's
go back to that: open code the ctx->pr condition and fire the exception
if we're not privileged. The difference from the code back then to what
we're doing now is an 'unlikely' compiler hint to ctx->pr and the use of
gen_priv_opc() instead of gen_priv_exception().

Fixes: Coverity CID 1490757
Cc: Matheus Ferst <matheus.ferst@eldorado.org.br>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
---
 target/ppc/translate/fixedpoint-impl.c.inc | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/target/ppc/translate/fixedpoint-impl.c.inc b/target/ppc/translate/fixedpoint-impl.c.inc
index db14d3bebc..a3ade4fe2b 100644
--- a/target/ppc/translate/fixedpoint-impl.c.inc
+++ b/target/ppc/translate/fixedpoint-impl.c.inc
@@ -79,8 +79,11 @@ static bool do_ldst_quad(DisasContext *ctx, arg_D *a, bool store, bool prefixed)
     REQUIRE_INSNS_FLAGS(ctx, 64BX);
 
     if (!prefixed && !(ctx->insns_flags2 & PPC2_LSQ_ISA207)) {
-        /* lq and stq were privileged prior to V. 2.07 */
-        REQUIRE_SV(ctx);
+        if (unlikely(ctx->pr)) {
+            /* lq and stq were privileged prior to V. 2.07 */
+            gen_priv_opc(ctx);
+            return true;
+        }
 
         if (ctx->le_mode) {
             gen_align_no_le(ctx);
-- 
2.36.1