Re: vrp bitfield miscompilation (WAS: [Regression] snd_emu10k1 doesn't work after GCC 4.2 upgrade)



Hans Petter Selasky wrote:
On Monday 28 May 2007 08:22, Yuriy Tsibizov wrote:
-----Original Message-----
From: Yuriy Tsibizov
Sent: Sunday, May 27, 2007 1:42 AM
To: Yuriy Tsibizov; kabaev@xxxxxxxxx
Cc: current@xxxxxxxxxxx
Subject: Re: [Regression] snd_emu10k1 doesn't work after GCC
4.2 upgrade

See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32100
Use of following variables _can_ be affected by above miscompilation
(these are signed single-bit variables):

amd64/amd64/mp_machdep.c: int cpu_present:1;
amd64/amd64/mp_machdep.c: int cpu_bsp:1;
amd64/amd64/mp_machdep.c: int cpu_disabled:1;
dev/acpica/acpi_pci_link.c: int l_routed:1;
dev/acpica/acpi_pci_link.c: int l_isa_irq:1;
dev/sound/isa/ess.c: int type, duplex:1, newspeed:1;
dev/sound/pci/emu10k1.c: int b16:1, stereo:1, busy:1, running:1,
ismaster:1;
dev/sound/pci/solo.c: int simplex_dir, type, duplex:1,
newspeed:1, dmasz[2];
dev/puc/puc.c: int p_hasintr:1;
dev/puc/puc_bfe.h: int sc_fastintr:1;
dev/puc/puc_bfe.h: int sc_leaving:1;
dev/puc/puc_bfe.h: int sc_polled:1;
dev/rp/rpvar.h: int rp_rts_iflow:1;
dev/rp/rpvar.h: int rp_disable_writes:1;
dev/rp/rpvar.h: int rp_cts:1;
dev/rp/rpvar.h: int rp_waiting:1;
dev/rp/rpvar.h: int rp_xmit_stopped:1;
dev/scc/scc_bfe.h: int m_attached:1;
dev/scc/scc_bfe.h: int m_fastintr:1;
dev/scc/scc_bfe.h: int m_hasintr:1;
dev/scc/scc_bfe.h: int m_probed:1;
dev/scc/scc_bfe.h: int m_sysdev:1;
dev/scc/scc_bfe.h: int ch_enabled:1;
dev/scc/scc_bfe.h: int ch_sysdev:1;
dev/scc/scc_bfe.h: int sc_fastintr:1;
dev/scc/scc_bfe.h: int sc_leaving:1;
dev/scc/scc_bfe.h: int sc_polled:1;
dev/uart/uart_bus.h: int sc_callout:1; /* This UART is
opened for callout. */
dev/uart/uart_bus.h: int sc_fastintr:1; /* This UART
uses fast interrupts. */
dev/uart/uart_bus.h: int sc_hwiflow:1; /* This UART has
HW input flow ctl. */
dev/uart/uart_bus.h: int sc_hwoflow:1; /* This UART has
HW output flow ctl. */
dev/uart/uart_bus.h: int sc_leaving:1; /* This UART is
going away. */
dev/uart/uart_bus.h: int sc_opened:1; /* This UART is
open for business. */
dev/uart/uart_bus.h: int sc_polled:1; /* This UART has
no interrupts. */
dev/uart/uart_bus.h: int sc_txbusy:1; /* This UART is
transmitting. */
fs/pseudofs/pseudofs_internal.h: int pvd_dead:1;
geom/part/g_part.h: int gpe_created:1; /* Entry is
newly created. */
geom/part/g_part.h: int gpe_deleted:1; /* Entry has
been deleted. */
geom/part/g_part.h: int gpe_modified:1; /* Entry has
been modified. */
geom/part/g_part.h: int gpt_isleaf:1; /* Cannot be
sub-partitioned. */
geom/part/g_part.h: int gpt_created:1; /* Newly
created. */
geom/part/g_part.h: int gpt_modified:1; /* Table changes
have been made. */
geom/part/g_part.h: int gpt_opened:1; /* Permissions
obtained. */
i386/i386/mp_machdep.c: int cpu_present:1;
i386/i386/mp_machdep.c: int cpu_bsp:1;
i386/i386/mp_machdep.c: int cpu_disabled:1;
i386/include/npx.h: int fp_sgn:1; /* mantissa sign */
sparc64/pci/psycho.c: int apb:1;
sparc64/pci/psycho.c: int ppb:1;

I can't say that there _is_ a miscompilation related to all variables in
this list.

Should most of them (I'm not shure for fp_sign) be changed to unsigned
int? With (signed) int these flags have values of (-1;0), with unsigned
int they will use more obvious (0;1) values.


Yuriy.

Interesting find. Another issue:

I've seen that the compile will round the memory size of a bit-fields down to the nearest byte, if you turn on optimization. I think you should use "uint8_t".

My memory is that bitfields are only defined as parts of an 'int'
in the standard and that using anything else is a gcc 'feature'.

This is a 14 year old memory (from my SCSI days) so it may not be true
now.



--HPS
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