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[riscv] Allow for a non-zero link-time address

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Using paging (rather than relocation records) will be easier on 64-bit
RISC-V if we place iPXE within the negative (kernel) virtual address
space.

Allow the link-time address to be non-zero and to vary between 32-bit
and 64-bit builds.  Choose addresses that are expected to be amenable
to the use of paging.

There is no particular need to use a non-zero address in the 32-bit
builds, but doing so allows us to validate that the relocation code is
handling this case correctly.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2025-05-01 14:24:33 +01:00
parent a4b5dd63c5
commit dad2060260
3 changed files with 19 additions and 4 deletions
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7
src/arch/riscv/scripts/sbi.lds
View File

@@ -5,10 +5,8 @@
SECTIONS {
/* Start at virtual address zero */
. = 0;
/* Weak symbols that need zero values if not otherwise defined */
saved_pos = .;
.weak 0x0 : {
_weak = .;
*(.weak)
@@ -16,6 +14,7 @@ SECTIONS {
_eweak = .;
}
_assert = ASSERT ( ( _weak == _eweak ), ".weak is non-zero length" );
_assert = ASSERT ( ( . == saved_pos ), ".weak altered current position" );
/* Prefix code */
.prefix : {
@@ -105,7 +104,7 @@ SECTIONS {
_ereloc = ( _reloc + __load_stop_reladyn - __load_start_reladyn );
/* Length of initialised data */
_sbi_filesz = ABSOLUTE ( _ereloc );
_sbi_filesz = ( ABSOLUTE ( _ereloc ) - ABSOLUTE ( _prefix ) );
/* Unwanted sections */
/DISCARD/ : {

8
src/arch/riscv32/Makefile.sbi
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@@ -1,5 +1,13 @@
# -*- makefile -*- : Force emacs to use Makefile mode
# Set base virtual address to 0xeb000000
#
# This is aligned to a 4MB boundary and so allows 4MB megapages to be
# used to map the iPXE binary. The address pattern is also easily
# recognisable if leaked to unexpected contexts.
#
LDFLAGS += --section-start=.prefix=0xeb000000
# Include generic SBI Makefile
#
MAKEDEPS += arch/riscv/Makefile.sbi

8
src/arch/riscv64/Makefile.sbi
View File

@@ -1,5 +1,13 @@
# -*- makefile -*- : Force emacs to use Makefile mode
# Set base virtual address to 0xffffffffeb000000
#
# This is aligned to a 2MB boundary and so allows 2MB megapages to be
# used to map the iPXE binary. The address pattern is also easily
# recognisable if leaked to unexpected contexts.
#
LDFLAGS += --section-start=.prefix=0xffffffffeb000000
# Include generic SBI Makefile
#
MAKEDEPS += arch/riscv/Makefile.sbi