binutils-gdb/gdb/testsuite/gdb.fortran/array-slices-sub-slices.exp

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# Copyright 2020-2021 Free Software Foundation, Inc.
gdb/fortran: Add support for Fortran array slices at the GDB prompt This commit brings array slice support to GDB. WARNING: This patch contains a rather big hack which is limited to Fortran arrays, this can be seen in gdbtypes.c and f-lang.c. More details on this below. This patch rewrites two areas of GDB's Fortran support, the code to extract an array slice, and the code to print an array. After this commit a user can, from the GDB prompt, ask for a slice of a Fortran array and should get the correct result back. Slices can (optionally) have the lower bound, upper bound, and a stride specified. Slices can also have a negative stride. Fortran has the concept of repacking array slices. Within a compiled Fortran program if a user passes a non-contiguous array slice to a function then the compiler may have to repack the slice, this involves copying the elements of the slice to a new area of memory before the call, and copying the elements back to the original array after the call. Whether repacking occurs will depend on which version of Fortran is being used, and what type of function is being called. This commit adds support for both packed, and unpacked array slicing, with the default being unpacked. With an unpacked array slice, when the user asks for a slice of an array GDB creates a new type that accurately describes where the elements of the slice can be found within the original array, a value of this type is then returned to the user. The address of an element within the slice will be equal to the address of an element within the original array. A user can choose to select packed array slices instead using: (gdb) set fortran repack-array-slices on|off (gdb) show fortran repack-array-slices With packed array slices GDB creates a new type that reflects how the elements of the slice would look if they were laid out in contiguous memory, allocates a value of this type, and then fetches the elements from the original array and places then into the contents buffer of the new value. One benefit of using packed slices over unpacked slices is the memory usage, taking a small slice of N elements from a large array will require (in GDB) N * ELEMENT_SIZE bytes of memory, while an unpacked array will also include all of the "padding" between the non-contiguous elements. There are new tests added that highlight this difference. There is also a new debugging flag added with this commit that introduces these commands: (gdb) set debug fortran-array-slicing on|off (gdb) show debug fortran-array-slicing This prints information about how the array slices are being built. As both the repacking, and the array printing requires GDB to walk through a multi-dimensional Fortran array visiting each element, this commit adds the file f-array-walk.h, which introduces some infrastructure to support this process. This means the array printing code in f-valprint.c is significantly reduced. The only slight issue with this commit is the "rather big hack" that I mentioned above. This hack allows us to handle one specific case, array slices with negative strides. This is something that I don't believe the current GDB value contents model will allow us to correctly handle, and rather than rewrite the value contents code right now, I'm hoping to slip this hack in as a work around. The problem is that, as I see it, the current value contents model assumes that an object base address will be the lowest address within that object, and that the contents of the object start at this base address and occupy the TYPE_LENGTH bytes after that. ( We do have the embedded_offset, which is used for C++ sub-classes, such that an object can start at some offset from the content buffer, however, the assumption that the object then occupies the next TYPE_LENGTH bytes is still true within GDB. ) The problem is that Fortran arrays with a negative stride don't follow this pattern. In this case the base address of the object points to the element with the highest address, the contents of the array then start at some offset _before_ the base address, and proceed for one element _past_ the base address. As the stride for such an array would be negative then, in theory the TYPE_LENGTH for this type would also be negative. However, in many places a value in GDB will degrade to a pointer + length, and the length almost always comes from the TYPE_LENGTH. It is my belief that in order to correctly model this case the value content handling of GDB will need to be reworked to split apart the value's content buffer (which is a block of memory with a length), and the object's in memory base address and length, which could be negative. Things are further complicated because arrays with negative strides like this are always dynamic types. When a value has a dynamic type and its base address needs resolving we actually store the address of the object within the resolved dynamic type, not within the value object itself. In short I don't currently see an easy path to cleanly support this situation within GDB. And so I believe that leaves two options, either add a work around, or catch cases where the user tries to make use of a negative stride, or access an array with a negative stride, and throw an error. This patch currently goes with adding a work around, which is that when we resolve a dynamic Fortran array type, if the stride is negative, then we adjust the base address to point to the lowest address required by the array. The printing and slicing code is aware of this adjustment and will correctly slice and print Fortran arrays. Where this hack will show through to the user is if they ask for the address of an array in their program with a negative array stride, the address they get from GDB will not match the address that would be computed within the Fortran program. gdb/ChangeLog: * Makefile.in (HFILES_NO_SRCDIR): Add f-array-walker.h. * NEWS: Mention new options. * f-array-walker.h: New file. * f-lang.c: Include 'gdbcmd.h' and 'f-array-walker.h'. (repack_array_slices): New static global. (show_repack_array_slices): New function. (fortran_array_slicing_debug): New static global. (show_fortran_array_slicing_debug): New function. (value_f90_subarray): Delete. (skip_undetermined_arglist): Delete. (class fortran_array_repacker_base_impl): New class. (class fortran_lazy_array_repacker_impl): New class. (class fortran_array_repacker_impl): New class. (fortran_value_subarray): Complete rewrite. (set_fortran_list): New static global. (show_fortran_list): Likewise. (_initialize_f_language): Register new commands. (fortran_adjust_dynamic_array_base_address_hack): New function. * f-lang.h (fortran_adjust_dynamic_array_base_address_hack): Declare. * f-valprint.c: Include 'f-array-walker.h'. (class fortran_array_printer_impl): New class. (f77_print_array_1): Delete. (f77_print_array): Delete. (fortran_print_array): New. (f_value_print_inner): Update to call fortran_print_array. * gdbtypes.c: Include 'f-lang.h'. (resolve_dynamic_type_internal): Call fortran_adjust_dynamic_array_base_address_hack. gdb/testsuite/ChangeLog: * gdb.fortran/array-slices-bad.exp: New file. * gdb.fortran/array-slices-bad.f90: New file. * gdb.fortran/array-slices-sub-slices.exp: New file. * gdb.fortran/array-slices-sub-slices.f90: New file. * gdb.fortran/array-slices.exp: Rewrite tests. * gdb.fortran/array-slices.f90: Rewrite tests. * gdb.fortran/vla-sizeof.exp: Correct expected results. gdb/doc/ChangeLog: * gdb.texinfo (Debugging Output): Document 'set/show debug fortran-array-slicing'. (Special Fortran Commands): Document 'set/show fortran repack-array-slices'.
2020-10-08 23:45:59 +08:00
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/> .
# Create a slice of an array, then take a slice of that slice.
if {[skip_fortran_tests]} { return -1 }
standard_testfile ".f90"
load_lib fortran.exp
if {[prepare_for_testing ${testfile}.exp ${testfile} ${srcfile} \
{debug f90}]} {
return -1
}
if ![fortran_runto_main] {
untested "could not run to main"
return -1
}
# gdb_breakpoint [gdb_get_line_number "Display Message Breakpoint"]
gdb_breakpoint [gdb_get_line_number "Stop Here"]
gdb_breakpoint [gdb_get_line_number "Final Breakpoint"]
# We're going to print some reasonably large arrays.
gdb_test_no_output "set print elements unlimited"
gdb_continue_to_breakpoint "Stop Here"
# Print a slice, capture the convenience variable name created.
set cmd "print array (1:10:2, 1:10:2)"
gdb_test_multiple $cmd $cmd {
-re "\r\n\\\$(\\d+) = .*\r\n$gdb_prompt $" {
set varname "\$$expect_out(1,string)"
}
}
# Now check that we can correctly extract all the elements from this
# slice.
for { set j 1 } { $j < 6 } { incr j } {
for { set i 1 } { $i < 6 } { incr i } {
set val [expr ((($i - 1) * 2) + (($j - 1) * 20)) + 1]
gdb_test "print ${varname} ($i,$j)" " = $val"
}
}
# Now take a slice of the slice.
gdb_test "print ${varname} (3:5, 3:5)" \
" = \\(\\(45, 47, 49\\) \\(65, 67, 69\\) \\(85, 87, 89\\)\\)"
# Now take a different slice of a slice.
set cmd "print ${varname} (1:5:2, 1:5:2)"
gdb_test_multiple $cmd $cmd {
-re "\r\n\\\$(\\d+) = \\(\\(1, 5, 9\\) \\(41, 45, 49\\) \\(81, 85, 89\\)\\)\r\n$gdb_prompt $" {
set varname "\$$expect_out(1,string)"
pass $gdb_test_name
}
}
# Now take a slice from the slice, of a slice!
set cmd "print ${varname} (1:3:2, 1:3:2)"
gdb_test_multiple $cmd $cmd {
-re "\r\n\\\$(\\d+) = \\(\\(1, 9\\) \\(81, 89\\)\\)\r\n$gdb_prompt $" {
set varname "\$$expect_out(1,string)"
pass $gdb_test_name
}
}
# And again!
set cmd "print ${varname} (1:2:2, 1:2:2)"
gdb_test_multiple $cmd $cmd {
-re "\r\n\\\$(\\d+) = \\(\\(1\\)\\)\r\n$gdb_prompt $" {
set varname "\$$expect_out(1,string)"
pass $gdb_test_name
}
}
# Test taking a slice with stride of a string. This isn't actually
# supported within gfortran (at least), but naturally drops out of how
# GDB models arrays and strings in a similar way, so we may as well
# test that this is still working.
gdb_test "print str (1:26:2)" " = 'acegikmoqsuwy'"
gdb_test "print str (26:1:-1)" " = 'zyxwvutsrqponmlkjihgfedcba'"
gdb_test "print str (26:1:-2)" " = 'zxvtrpnljhfdb'"
# Now test the memory requirements of taking a slice from an array.
# The idea is that we shouldn't require more memory to extract a slice
# than the size of the slice.
#
# This will only work if array repacking is turned on, otherwise GDB
# will create the slice by generating a new type that sits over the
# existing value in memory.
gdb_test_no_output "set fortran repack-array-slices on"
set element_size [get_integer_valueof "sizeof (array (1,1))" "unknown"]
set slice_size [expr $element_size * 4]
gdb_test_no_output "set max-value-size $slice_size"
gdb_test "print array (1:2, 1:2)" "= \\(\\(1, 2\\) \\(11, 12\\)\\)"
gdb_test "print array (2:3, 2:3)" "= \\(\\(12, 13\\) \\(22, 23\\)\\)"
gdb_test "print array (2:5:2, 2:5:2)" "= \\(\\(12, 14\\) \\(32, 34\\)\\)"