When `info float` is used on an AMD64 system, GDB prints
floating-point values of x87 registers with raw contents like
0x361a867a8e0527397ce0 or 0xc4f988454a1ddd3cfdab wrongly.
This happens due to truncation to double, after which the former
becomes 0.0, and the latter becomes negative infinity. This is caused
by failed detection of x86-64 host, which results in setting
gdb_host_{float,double,long_double}_format to zeros.
This commit fixes this misdetection, and adds a test to make sure
future commits don't introduce a regression here.
gdb/ChangeLog:
2015-12-09 Ruslan Kabatsayev <b7.10110111@gmail.com>
PR gdb/18702
* configure.host: Fix detection of x86_64 host when setting
floatformats.
gdb/testsuite/ChangeLog:
2015-12-09 Ruslan Kabatsayev <b7.10110111@gmail.com>
Pedro Alves <pedro@redhat.com>
PR gdb/18702
Add checking of floatformats setup on x86_64 hosts.
* gdb.arch/i386-float.S (main): Load bigval and smallval.
(smallval, bigval): New labels/constants.
* gdb.arch/i386-float.exp: Use with_test_prefix and test "info
float" after loading bigval and smallval.
Consider the following simple program:
.globl _start
.text
_start:
fldt val
.data
val: .byte 0x00,0x00,0x45,0x07,0x11,0x19,0x22,0xe9,0xfe,0xbf
With current GDB on x86-64 GNU/Linux hosts, after the moment the fldt
command has been executed the register st(0) looks like this,
according to the “info regs” output (TOP=7):
R7: Valid 0xffffffbffffffffeffffffe922191107450000 -0.910676542908976927
which is clearly wrong (just count its length). The problem is due to
the printf statement (see patch) printing a promoted integer value of
a char argument "raw[i]", and, since char is signed on x86-64
GNU/Linux, the erroneous “ffffff” are printed for the first three
bytes which turn out to be "negative". The fix is to use gdb_byte
instead which is unsigned (and is the type of value_contents(), the
type to be used for raw target bytes anyway). After the fix the value
will be printed correctly:
R7: Valid 0xbffee922191107450000 -0.910676542908976927
gdb/
2013-04-19 Vladimir Kargov <kargov@gmail.com>
Pedro Alves <palves@redhat.com>
* i387-tdep.c (i387_print_float_info): Use gdb_byte for pointer to
value contents.
gdb/testsuite/
2013-04-19 Vladimir Kargov <kargov@gmail.com>
Pedro Alves <palves@redhat.com>
* gdb.arch/i386-float.S: New file.
* gdb.arch/i386-float.exp: New file.
