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Respect count in TCB_Write/ReadRegisters via loop

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Previously TCB_WriteRegisters/ReadRegisters ignored the count parameter
and unconditionally copied the entire seL4_UserContext, this leads to
unnecessary overhead for VMM operations.

This addresses issue #1085

Signed-off-by: Yifei Zhan <yifei@zhan.science>
This commit is contained in:
yifei@zhan.science
2026-04-09 00:03:42 -04:00
committed by Indan Zupancic
parent 061017b242
commit 19a520a22b
1 changed files with 33 additions and 12 deletions
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45
libsel4/tools/syscall_stub_gen.py
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@@ -698,10 +698,25 @@ def generate_stub(arch, wordsize, interface_name, method_name, method_id, input_
result.append("\tmr%d = %s;" % (i, input_expressions[i]))
else:
result.append("\tmr%d = 0;" % i)
# Initialise buffered parameters
for i in range(num_mrs, len(input_expressions)):
result.append("\tseL4_SetMR(%d, %s);" % (i, input_expressions[i]))
result.append("")
TCB_writeRegister_can_loop = (
method_name == "WriteRegisters" and
interface_name == "seL4_TCB" and
num_mrs >= 2
)
if TCB_writeRegister_can_loop:
# First 2 registers are always passed by mrs, thus initialise buffered
# parameters only when requesting more than 2 registers
regs_by_mrs = num_mrs - 2
result.append("\tfor (seL4_Word i = %d; i < count; i++) {" % regs_by_mrs)
result.append("\t\tseL4_SetMR(i + 2, ((seL4_Word*)&%s)[i - %d]);" %
(input_expressions[num_mrs], regs_by_mrs))
result.append("\t}")
result.append("")
else:
# Initialise buffered parameters
for i in range(num_mrs, len(input_expressions)):
result.append("\tseL4_SetMR(%d, %s);" % (i, input_expressions[i]))
result.append("")
#
# Generate the call.
@@ -747,15 +762,25 @@ def generate_stub(arch, wordsize, interface_name, method_name, method_id, input_
for i in range(MAX_MESSAGE_LENGTH):
if i < num_mrs:
source_words["w%d" % i] = "mr%d" % i
else:
elif method_name != "ReadRegisters" or num_mrs < 2:
source_words["w%d" % i] = "seL4_GetMR(%d)" % i
unmashalled_params = generate_unmarshal_expressions(output_params, wordsize)
for (param, words) in unmashalled_params:
if param.type.pass_by_reference():
members = struct_members(param.type, structs)
for i in range(len(words)):
result.append("\t%s->%s = %s;" %
(param.name, members[i], words[i] % source_words))
if method_name == "ReadRegisters" and num_mrs >= 2:
for i in range(len(source_words)):
result.append("\t%s->%s = %s;" %
(param.name, members[i], words[i] % source_words))
result.append("\tfor (seL4_Word i = %d; i < count; i++) {" % num_mrs)
result.append("\t\t((seL4_Word *) &%s->%s)[i - %d] = seL4_GetMR(i);" %
(param.name, members[num_mrs], num_mrs))
result.append("\t}")
else:
for i in range(len(words)):
result.append("\t%s->%s = %s;" %
(param.name, members[i], words[i] % source_words))
else:
if param.type.double_word:
result.append("\tresult.%s = ((%s)%s + ((%s)%s << 32));" %
@@ -764,10 +789,6 @@ def generate_stub(arch, wordsize, interface_name, method_name, method_id, input_
else:
for word in words:
result.append("\tresult.%s = %s;" % (param.name, word % source_words))
#
# }
#
result.append("\treturn result;")
result.append("}")