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[PATCHv3] exynos4210_gic: Suppress gcc9 format-truncation warnings

From: David Gibson
Subject: [PATCHv3] exynos4210_gic: Suppress gcc9 format-truncation warnings
Date: Mon, 2 Dec 2019 17:08:06 +1100

exynos4210_gic_realize() prints the number of cpus into some temporary
buffers, but it only allows 3 bytes space for it.  That's plenty:
existing machines will only ever set this value to EXYNOS4210_NCPUS
(2).  But the compiler can't always figure that out, so some[*] gcc9
versions emit -Wformat-truncation warnings.

We can fix that by hinting the constraint to the compiler with a
suitably placed assert().

[*] The bizarre thing here, is that I've long gotten these warnings
    compiling in a 32-bit x86 container as host - Fedora 30 with
    gcc-9.2.1-1.fc30.i686 - but it compiles just fine on my normal
    x86_64 host - Fedora 30 with and gcc-9.2.1-1.fc30.x86_64.

Signed-off-by: David Gibson <address@hidden>
Reviewed-by: Philippe Mathieu-Daudé <address@hidden>

Peter, up to you if you squeeze this in for qemu-4.2 or leave it until 5.0

Changes since v2:
 * Moved the assert outside the for loop using a trick suggested by
   Richard Henderson
Changes since v1:
 * Used an assert to hint the compiler, instead of increasing the
   buffer size.

 hw/intc/exynos4210_gic.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/hw/intc/exynos4210_gic.c b/hw/intc/exynos4210_gic.c
index a1b699b6ba..ddd006aca6 100644
--- a/hw/intc/exynos4210_gic.c
+++ b/hw/intc/exynos4210_gic.c
@@ -293,6 +293,7 @@ static void exynos4210_gic_realize(DeviceState *dev, Error 
     char cpu_alias_name[sizeof(cpu_prefix) + 3];
     char dist_alias_name[sizeof(cpu_prefix) + 3];
     SysBusDevice *gicbusdev;
+    uint32_t n = s->num_cpu;
     uint32_t i;
     s->gic = qdev_create(NULL, "arm_gic");
@@ -313,7 +314,14 @@ static void exynos4210_gic_realize(DeviceState *dev, Error 
     memory_region_init(&s->dist_container, obj, "exynos4210-dist-container",
-    for (i = 0; i < s->num_cpu; i++) {
+    /*
+     * This clues in gcc that our on-stack buffers do, in fact have
+     * enough room for the cpu numbers.  gcc 9.2.1 on 32-bit x86
+     * doesn't figure this out, otherwise and gives spurious warnings.
+     */
+    assert(n <= EXYNOS4210_NCPUS);
+    for (i = 0; i < n; i++) {
         /* Map CPU interface per SMP Core */
         sprintf(cpu_alias_name, "%s%x", cpu_prefix, i);
         memory_region_init_alias(&s->cpu_alias[i], obj,

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