[SeaBIOS] Re: [PATCH] std/tcg: Replace zero-length array with flexible-array member
On 3/3/20 11:50 AM, Paul Menzel wrote:
Date: Tue, 3 Mar 2020 16:24:46 +0100
GCC 10 gives the warnings below:
In file included from out/ccode32flat.o.tmp.c:54:
./src/tcgbios.c: In function 'tpm20_write_EfiSpecIdEventStruct':
./src/tcgbios.c:290:30: warning: array subscript '() +
4294967295' is outside the bounds of an interior zero-length array 'struct
TCG_EfiSpecIdEventAlgorithmSize[0]' [-Wzero-length-bounds]
290 | event.hdr.digestSizes[count].algorithmId =
be16_to_cpu(sel->hashAlg);
| ~^~~
In file included from ./src/tcgbios.c:22,
from out/ccode32flat.o.tmp.c:54:
./src/std/tcg.h:527:7: note: while referencing 'digestSizes'
527 | } digestSizes[0];
| ^~~
In file included from out/ccode32flat.o.tmp.c:54:
./src/tcgbios.c:291:30: warning: array subscript '() +
4294967295' is outside the bounds of an interior zero-length array 'struct
TCG_EfiSpecIdEventAlgorithmSize[0]' [-Wzero-length-bounds]
291 | event.hdr.digestSizes[count].digestSize = hsize;
| ~^~~
In file included from ./src/tcgbios.c:22,
from out/ccode32flat.o.tmp.c:54:
./src/std/tcg.h:527:7: note: while referencing 'digestSizes'
527 | } digestSizes[0];
| ^~~
[Description copied from Gustavo A. R. Silva
from his Linux kernel commits.]
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array
member [1], introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
This issue was found with the help of Coccinelle.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
Signed-off-by: Paul Menzel
It gives the same size of structure either way.
Reviewed-by: Stefan Berger
---
src/std/tcg.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/std/tcg.h b/src/std/tcg.h
index 1cc1c92..1c9eeb4 100644
--- a/src/std/tcg.h
+++ b/src/std/tcg.h
@@ -524,7 +524,7 @@ struct TCG_EfiSpecIdEventStruct {
struct TCG_EfiSpecIdEventAlgorithmSize {
u16 algorithmId;
u16 digestSize;
-} digestSizes[0];
+} digestSizes[];
/*
u8 vendorInfoSize;
u8 vendorInfo[0];
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[SeaBIOS] Re: [PATCH] std/tcg: Replace zero-length array with flexible-array member
On Tue, Mar 3, 2020 at 7:08 PM Philippe Mathieu-Daudé wrote:
>
> Hello Paul,
>
> On 3/3/20 5:50 PM, Paul Menzel wrote:
> > Date: Tue, 3 Mar 2020 16:24:46 +0100
> >
> > GCC 10 gives the warnings below:
> >
> > In file included from out/ccode32flat.o.tmp.c:54:
> > ./src/tcgbios.c: In function 'tpm20_write_EfiSpecIdEventStruct':
> > ./src/tcgbios.c:290:30: warning: array subscript '() +
> > 4294967295' is outside the bounds of an interior zero-length array 'struct
> > TCG_EfiSpecIdEventAlgorithmSize[0]' [-Wzero-length-bounds]
> >290 | event.hdr.digestSizes[count].algorithmId =
> > be16_to_cpu(sel->hashAlg);
> >| ~^~~
> > In file included from ./src/tcgbios.c:22,
> > from out/ccode32flat.o.tmp.c:54:
> > ./src/std/tcg.h:527:7: note: while referencing 'digestSizes'
> >527 | } digestSizes[0];
> >| ^~~
> > In file included from out/ccode32flat.o.tmp.c:54:
> > ./src/tcgbios.c:291:30: warning: array subscript '() +
> > 4294967295' is outside the bounds of an interior zero-length array 'struct
> > TCG_EfiSpecIdEventAlgorithmSize[0]' [-Wzero-length-bounds]
> >291 | event.hdr.digestSizes[count].digestSize = hsize;
> >| ~^~~
> > In file included from ./src/tcgbios.c:22,
> > from out/ccode32flat.o.tmp.c:54:
> > ./src/std/tcg.h:527:7: note: while referencing 'digestSizes'
> >527 | } digestSizes[0];
> >| ^~~
> >
> > [Description copied from Gustavo A. R. Silva
> > from his Linux kernel commits.]
> >
> > The current codebase makes use of the zero-length array language
> > extension to the C90 standard, but the preferred mechanism to declare
> > variable-length types such as these ones is a flexible array
> > member [1], introduced in C99:
> >
> > struct foo {
> > int stuff;
> > struct boo array[];
> > };
> >
> > By making use of the mechanism above, we will get a compiler warning
> > in case the flexible array does not occur last in the structure, which
> > will help us prevent some kind of undefined behavior bugs from being
> > inadvertently introduced[3] to the codebase from now on.
>
> Assuming this comment is also part of the Linux kernel commit, can we
> drop the '[3]' marker?
Assuming the maintainer can do this trivial change:
Reviewed-by: Philippe Mathieu-Daudé
>
> >
> > Also, notice that, dynamic memory allocations won't be affected by
> > this change:
> >
> > "Flexible array members have incomplete type, and so the sizeof operator
> > may not be applied. As a quirk of the original implementation of
> > zero-length arrays, sizeof evaluates to zero."[1]
> >
> > This issue was found with the help of Coccinelle.
> >
> > [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> >
> > Signed-off-by: Paul Menzel
> > ---
> > src/std/tcg.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/src/std/tcg.h b/src/std/tcg.h
> > index 1cc1c92..1c9eeb4 100644
> > --- a/src/std/tcg.h
> > +++ b/src/std/tcg.h
> > @@ -524,7 +524,7 @@ struct TCG_EfiSpecIdEventStruct {
> > struct TCG_EfiSpecIdEventAlgorithmSize {
> > u16 algorithmId;
> > u16 digestSize;
> > -} digestSizes[0];
> > +} digestSizes[];
> > /*
> > u8 vendorInfoSize;
> > u8 vendorInfo[0];
> >
> >
> > ___
> > SeaBIOS mailing list -- seabios@seabios.org
> > To unsubscribe send an email to seabios-le...@seabios.org
> >
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[SeaBIOS] Re: [PATCH] std/tcg: Replace zero-length array with flexible-array member
Hello Paul,
On 3/3/20 5:50 PM, Paul Menzel wrote:
Date: Tue, 3 Mar 2020 16:24:46 +0100
GCC 10 gives the warnings below:
In file included from out/ccode32flat.o.tmp.c:54:
./src/tcgbios.c: In function 'tpm20_write_EfiSpecIdEventStruct':
./src/tcgbios.c:290:30: warning: array subscript '() +
4294967295' is outside the bounds of an interior zero-length array 'struct
TCG_EfiSpecIdEventAlgorithmSize[0]' [-Wzero-length-bounds]
290 | event.hdr.digestSizes[count].algorithmId =
be16_to_cpu(sel->hashAlg);
| ~^~~
In file included from ./src/tcgbios.c:22,
from out/ccode32flat.o.tmp.c:54:
./src/std/tcg.h:527:7: note: while referencing 'digestSizes'
527 | } digestSizes[0];
| ^~~
In file included from out/ccode32flat.o.tmp.c:54:
./src/tcgbios.c:291:30: warning: array subscript '() +
4294967295' is outside the bounds of an interior zero-length array 'struct
TCG_EfiSpecIdEventAlgorithmSize[0]' [-Wzero-length-bounds]
291 | event.hdr.digestSizes[count].digestSize = hsize;
| ~^~~
In file included from ./src/tcgbios.c:22,
from out/ccode32flat.o.tmp.c:54:
./src/std/tcg.h:527:7: note: while referencing 'digestSizes'
527 | } digestSizes[0];
| ^~~
[Description copied from Gustavo A. R. Silva
from his Linux kernel commits.]
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array
member [1], introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Assuming this comment is also part of the Linux kernel commit, can we
drop the '[3]' marker?
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
This issue was found with the help of Coccinelle.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
Signed-off-by: Paul Menzel
---
src/std/tcg.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/std/tcg.h b/src/std/tcg.h
index 1cc1c92..1c9eeb4 100644
--- a/src/std/tcg.h
+++ b/src/std/tcg.h
@@ -524,7 +524,7 @@ struct TCG_EfiSpecIdEventStruct {
struct TCG_EfiSpecIdEventAlgorithmSize {
u16 algorithmId;
u16 digestSize;
-} digestSizes[0];
+} digestSizes[];
/*
u8 vendorInfoSize;
u8 vendorInfo[0];
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