[PULL 05/41] ppc/pnv: use a do-while() loop in pnv_phb3_translate_tve()

["Cédric Le Goater" <clg@kaod.org>]

From: Daniel Henrique Barboza <danielhb413@gmail.com>

The 'taddr' variable is left unintialized, being set only inside the
"while ((lev--) >= 0)" loop where we get the TCE address. The 'lev' var
is an int32_t that is being initiliazed by the GETFIELD() macro, which
returns an uint64_t.

For a human reader this means that 'lev' will always be positive or zero.
But some compilers may beg to differ. 'lev' being an int32_t can in theory
be set as negative, and the "while ((lev--) >= 0)" loop might never be
reached, and 'taddr' will be left unitialized. This can cause phb3_error()
to use 'taddr' uninitialized down below:

if ((is_write & !(tce & 2)) || ((!is_write) && !(tce & 1))) {
    phb3_error(phb, "TCE access fault at 0x%"PRIx64, taddr);

A quick way of fixing it is to use a do/while() loop. This will keep the
same semanting as the existing while() loop does and the compiler will
understand that 'taddr' will be initialized at least once.

Suggested-by: Matheus K. Ferst <matheus.ferst@eldorado.org.br>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/573
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20220127122234.842145-2-danielhb413@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
---
 hw/pci-host/pnv_phb3.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/hw/pci-host/pnv_phb3.c b/hw/pci-host/pnv_phb3.c
index a757f1a58ec8..aafd46b635e8 100644
--- a/hw/pci-host/pnv_phb3.c
+++ b/hw/pci-host/pnv_phb3.c
@@ -792,7 +792,9 @@ static void pnv_phb3_translate_tve(PnvPhb3DMASpace *ds, hwaddr addr,
         sh = tbl_shift * lev + tce_shift;
 
         /* TODO: Multi-level untested */
-        while ((lev--) >= 0) {
+        do {
+            lev--;
+
             /* Grab the TCE address */
             taddr = base | (((addr >> sh) & ((1ul << tbl_shift) - 1)) << 3);
             if (dma_memory_read(&address_space_memory, taddr, &tce,
@@ -813,7 +815,7 @@ static void pnv_phb3_translate_tve(PnvPhb3DMASpace *ds, hwaddr addr,
             }
             sh -= tbl_shift;
             base = tce & ~0xfffull;
-        }
+        } while (lev >= 0);
 
         /* We exit the loop with TCE being the final TCE */
         if ((is_write & !(tce & 2)) || ((!is_write) && !(tce & 1))) {
-- 
2.34.1